[OTel] Add logstash exporter logic

[edmocosta]

Proposed commit message

This PR implements the logstash exporter logic, which includes:

• Batch creation from the plog data.
• Feed the logstash client workers queue.
• Wait and process the batch results, handling client retries (re-submitting the batch to the workers queue, as the backoff delay is already applied by the clients).
• Return a proper result to otelconsumer.

A few considerations:

• The exporter's ConsumeLogs response is sync, and it returns to the actual batch processing results, so the otelconsumer outcome is correct.
• The workers queue is sized as the the number of outputs.Client created by the otelconsumer, which given the sync ConsumeLogs nature, should be enough. A few adjusts might be necessary after benchmarking it, but it's not an issue at the moment.
• When the batch is dropped internally on the exporter, it returns a consumererror.NewPermanent, which leads the otelconsumer to also drop the batch on the beats side. Besides that, all other flow errors are being wrapped into consumererror.NewLogs.

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

How to test this PR locally

Run am agent filebeat in OTel mode, adding on the pipeline a logstash output configuration.

Related issues

Use cases

Screenshots

Logs

[github-actions]

🤖 GitHub comments

Expand to view the GitHub comments

Just comment with:

• run docs-build : Re-trigger the docs validation. (use unformatted text in the comment!)

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @edmocosta? 🙏.
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
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[edmocosta]

@elastic/beats-tech-leads could you please take a look at it so we can merge it?

[cmacknz]

Approving go.mod changes