feat(gcp_cloud_storage sink): add content_type option

[AnuragEkkati]

Summary

This PR Adds a "content_type" configuration option to the "gcp_cloud_storage" sink to allow overriding the MIME type set on uploaded GCS objects (e.g. text/plain; charset=utf-8). When not specified, the sink continues to use the encoder-derived content type which is the existing behavior.

Vector configuration

data_dir: /tmp/vector-data

sources:
  in:
    type: stdin

sinks:
  gcs:
    type: gcp_cloud_storage
    inputs: [in]
    bucket: ${GCS_BUCKET}
    key_prefix: "vector/test/"
    content_type: "text/plain; charset=utf-8"

    encoding:
      codec: text
      only_fields: ["message"]

    batch:
      max_bytes: 1000000
      timeout_secs: 2

    compression: none

How did you test this PR?

Ran unit tests:

• cargo test gcs_content_type_ (covers default/custom/invalid cases)

Manual verification:

Ran Vector locally and confirmed newly created objects in GCS had:

• Content-Type: text/plain; charset=utf-8 when content_type is set
• Content-Type: text/plain when content_type is not set

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

AI Assistance

Cursor AI : GPT-5 to check if any corner cases exists. Make sure my style is not out of order with existing style

References

• Closes: Feature Request: Add content_type option to gcp_cloud_storage sink #24410
• Related: Feature Request: Add content_type option to gcp_cloud_storage sink #24410
• Related: Feature Request: Add content_type option to gcp_cloud_storage sink #24410

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[AnuragEkkati]

I have read the CLA Document and I hereby sign the CLA

[thomasqueirozb]

Thanks!