Add Support for writing to Prometheus

[AncientPatata]

Issue Description

• Description of the issue:
  I'm trying to import Prometheus data that I've exported using Sling to an S3 bucket back into another (fresh) Prometheus deployment. The Data was exported to a CSV, and I managed to export everything by setting the source to '{name!=""}', I'm trying to do a similar thing for imports, using the official Docker image, but it's not been working for me, it keeps crashing while trying to format the target object.

  sling:
    image: slingdata/sling
    container_name: metrics_importer
    env_file: "./sling.env"
    depends_on:
      - prometheus
    networks: 
      - monitoring 
    command:
      - run
      - --src-conn
      - AWS_S3
      - --src-stream
      - test.csv
      - --tgt-conn
      - PROMETHEUS
      - --tgt-object
      - '{__name__!=""}'
      - --mode
      - full-refresh
      - -d

but it's not been

• Sling version (sling --version):
  Version : 1.2.23

• Operating System (linux, mac, windows):
  linux (Official Docker container)

• Replication Configuration:

None

• Log Output (please run command with -d):

2024-11-25 09:14:57 DBG opened "s3" connection (conn-s3-BIm)
2024-11-25 09:14:57 WRN Could not successfully get format values. Blank values for: object_schema
2024-11-25 09:14:57 DBG Could not successfully format target object name. Blank values for: __name__!=""
fatal:
--- proc.go:271 main ---
--- sling_cli.go:452 main ---
--- sling_cli.go:496 cliInit ---
panic occurred! "invalid memory address or nil pointer dereference"
goroutine 1 [running]:
runtime/debug.Stack()
        /github/sling-cli/_work/_tool/go/1.22.6/x64/src/runtime/debug/stack.go:24 +0x5e
main.processRun.func1()
        /github/sling-cli/_work/sling-cli/sling-cli/cmd/sling/sling_run.go:46 +0x38
panic({0x2fc5d40?, 0x6931470?})
        /github/sling-cli/_work/_tool/go/1.22.6/x64/src/runtime/panic.go:770 +0x132
github.com/slingdata-io/sling-cli/core/sling.(*Config).Prepare(0xc0013b2008)
        /github/sling-cli/_work/sling-cli/sling-cli/core/sling/config.go:581 +0x33c9
main.runTask(0xc0013b2008, 0xc0013be000)
        /github/sling-cli/_work/sling-cli/sling-cli/cmd/sling/sling_run.go:328 +0x16a
main.processRun(0x69954c0)
        /github/sling-cli/_work/sling-cli/sling-cli/cmd/sling/sling_run.go:216 +0x2350
github.com/flarco/g.CliProcess()
        /home/larco/go/pkg/mod/github.com/flarco/[email protected]/cli.go:286 +0x43b
main.cliInit(0x2e50ce0?)
        /github/sling-cli/_work/sling-cli/sling-cli/cmd/sling/sling_cli.go:488 +0x205
main.main()
        /github/sling-cli/_work/sling-cli/sling-cli/cmd/sling/sling_cli.go:452 +0x1fc

[flarco]

Sling does not support importing into Prom at the moment. Will add an error for this.