Add dropbox document loader docs

docs/core_docs/docs/integrations/document_loaders/web_loaders/dropbox.mdx

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-// documentation goes here
+---
+hide_table_of_contents: true
+sidebar_class_name: node-only
+---
+
+# Dropbox Loader
+
+The `DropboxLoader` allows you to load documents from Dropbox into your LangChain applications. It retrieves files or directories from your Dropbox account and converts them into documents ready for processing.
+
+## Overview
+
+Dropbox is a file hosting service that brings all your files—traditional documents, cloud content, and web shortcuts—together in one place. With the `DropboxLoader`, you can seamlessly integrate Dropbox file retrieval into your projects.
+
+## Setup
+
+1. Create a dropbox app, using the [Dropbox App Console](https://www.dropbox.com/developers/apps/create).
+2. Ensure the app has the `files.metadata.read`, `files.content.read` scope permissions:
+3. Generate the access token from the Dropbox App Console.
+4. To use this loader, you'll need to have Unstructured already set up and ready to use at an available URL endpoint. It can also be configured to run locally.
+   See the docs [here](https://www.dropbox.com/developers/apps/create) for information on how to do that.
+5. Install the necessary packages:
+
+   ```bash npm2yarn
+   npm install @langchain/community @langchain/core dropbox
+   ```
+
+## Usage
+
+### Loading Specific Files
+
+To load specific files from Dropbox, specify the file paths:
+
+```typescript
+import { DropboxLoader } from "@langchain/community/document_loaders/web/dropbox";
+
+const loader = new DropboxLoader({
+  clientOptions: {
+    accessToken: "your-dropbox-access-token",
+  },
+  unstructuredOptions: {
+    apiUrl: "http://localhost:8000/general/v0/general", // Replace with your Unstructured API URL
+  },
+  filePaths: ["/path/to/file1.txt", "/path/to/file2.pdf"], // Replace with file paths on Dropbox.
+});
+
+const docs = await loader.load();
+console.log(docs);
+```
+
+### Loading Files from a Directory
+
+To load all files from a specific directory, provide the `folderPath` and set the `mode` to `"directory"`. Set `recursive` to `true` to traverse subdirectories:
+
+```typescript
+import { DropboxLoader } from "@langchain/community/document_loaders/web/dropbox";
+
+const loader = new DropboxLoader({
+  clientOptions: {
+    accessToken: "your-dropbox-access-token",
+  },
+  unstructuredOptions: {
+    apiUrl: "http://localhost:8000/general/v0/general",
+  },
+  folderPath: "/path/to/folder",
+  recursive: true, // Load documents found in subdirectories
+  mode: "directory",
+});
+
+const docs = await loader.load();
+console.log(docs);
+```
+
+### Streaming Documents
+
+To process large datasets efficiently, use the `loadLazy` method to stream documents asynchronously:
+
+```typescript
+import { DropboxLoader } from "@langchain/community/document_loaders/web/dropbox";
+
+const loader = new DropboxLoader({
+  clientOptions: {
+    accessToken: "your-dropbox-access-token",
+  },
+  unstructuredOptions: {
+    apiUrl: "http://localhost:8000/general/v0/general",
+  },
+  folderPath: "/large/dataset",
+  recursive: true,
+  mode: "directory",
+});
+
+for await (const doc of loader.loadLazy()) {
+  // Process each document as it's loaded
+  console.log(doc);
+}
+```
+
+### Authentication with Environment Variables
+
+You can set the `DROPBOX_ACCESS_TOKEN` environment variable instead of passing the access token in `clientOptions`:
+
+```bash
+export DROPBOX_ACCESS_TOKEN=your-dropbox-access-token
+```
+
+Then initialize the loader without specifying `accessToken`:
+
+```typescript
+import { DropboxLoader } from "@langchain/community/document_loaders/web/dropbox";
+
+const loader = new DropboxLoader({
+  clientOptions: {},
+  unstructuredOptions: {
+    apiUrl: "http://localhost:8000/general/v0/general",
+  },
+  filePaths: ["/important/notes.txt"],
+});
+
+const docs = await loader.load();
+console.log(docs[0].pageContent);
+```
+
+## Configuration Options
+
+Here are the configuration options for the `DropboxLoader`:
+
+| Option                | Type                                 | Description                                                                                                                                                                                                                        |
+| --------------------- | ------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `clientOptions`       | `DropboxOptions`                     | Configuration options for initializing the Dropbox client, including authentication details. Refer to the [Dropbox SDK Documentation](https://dropbox.github.io/dropbox-sdk-js/Dropbox.html#Dropbox__anchor) for more information. |
+| `unstructuredOptions` | `UnstructuredLoaderOptions`          | Options for the `UnstructuredLoader` used to process downloaded files. Includes the `apiUrl` for your Unstructured server.                                                                                                         |
+| `folderPath`          | `string` (optional)                  | The path to the folder in Dropbox from which to load files. Defaults to the root folder (`""`) if not specified.                                                                                                                   |
+| `filePaths`           | `string[]` (optional)                | An array of specific file paths in Dropbox to load. Required if `mode` is set to `"file"`.                                                                                                                                         |
+| `recursive`           | `boolean` (optional)                 | Indicates whether to recursively traverse folders when `mode` is `"directory"`. Defaults to `false`.                                                                                                                               |
+| `mode`                | `"file"` or `"directory"` (optional) | The mode of operation. Set to `"file"` to load specific files or `"directory"` to load all files in a directory. Defaults to `"file"`.                                                                                             |
+
+## API References
+
+- [Dropbox SDK for JavaScript](https://github.com/dropbox/dropbox-sdk-js)