Support for keying messages by id and partition key

[cacodev]

## Problem Statement
I want to stream my cosmos data to a Kafka topic. I need the Kafka messages to be keyed with my document id plus the partition key. Having my topic messages keyed this way will allow for other processes to easily join my topic to other topics in my organization.

## Proposed Solution
My ideal solution would be to do this using the connector transforms (SMTs). This post seems to suggest that it is not possible, however, because the message is handed off to the transform as a string, not a JSON structure: #159 (comment)

## Alternative Solutions
An alternate solution would be to alter the message key options to select the Id and Partition key by field name.

## Additional context
I was very frustrated to learn that I could not do this with SMTs. I spent a lot of time debugging this and comparing with other connectors in my org. At the very least - can a note or warning be added to the documentation to save someone else the heart burn?

Next Steps

• Team consensus to proceed
• Schedule Design Session
• Complete Design Review

[jmorg98]

+1 to this