[filebeat] Add E2E testing for filebeat in otel mode

[khushijain21]

Proposed commit message

This adds. E2E test for filebeat in otel mode and confirms all the log records are indexed.

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.

How to test this PR locally

cd x-pack/filebeat
mage build
mage docker:composeUp
go test -run TestFilebeatOTelE2E -tags integration ./tests/integration

Related issues

Related to https://github.com/elastic/ingest-dev/issues/4595

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @khushijain21? 🙏.
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/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

Found an issue with the test that we should either address in this PR or agree on a follow up.