x-pack/filebeat/input/gcs: add support for CSV decoding

[efd6]

Proposed commit message

The test file txn.csv.gz was obtained from https://netskopepartnerlogfilebucket.s3.amazonaws.com/txn-1722875066329034-fe10b6a23cc643c4b282e6190de2352d.csv.gz

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• For [Netskope] Test ingestion of compressed Netskope cloud storage logs integrations#10744

Use cases

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Logs

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @efd6? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[elasticmachine]

Pinging @elastic/security-service-integrations (Team:Security-Service Integrations)

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b i10744-gcs upstream/i10744-gcs
git merge upstream/main
git push upstream i10744-gcs

[ShourieG]

Suggested change

	// newParquetDecoder creates a new CSV decoder.
	// csvDecoder creates a new CSV decoder.

[ShourieG]

Suggested change

	// close closes the parquet decoder and releases the resources.
	// close closes the csv decoder and releases the resources.

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b i10744-gcs upstream/i10744-gcs
git merge upstream/main
git push upstream i10744-gcs

[ShourieG]

Nits only & conflict resolution, since it's similar to #40978. Approving from my end.