Add Elastic Infra Metrics processor to otel mode

[andrzej-stencel]

What does this PR do?

This PR makes the Elastic Infra Metrics processor available to users running Elastic Agent in otel mode.

Why is it important?

The processor translates OTel native metrics to those understood by the Elastic system integration.

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/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

No impact expected.

How to test this PR locally

1. Build the agent locally (see docs)
2. Unpack the .tar.gz archive in build/distributions
3. Run the built binary with `build/distributions/elastic-agent-*/elastic-agent otel --config internal/pkg/otel/testdata/all-components.yml

Related issues

• Make elasticinframetricsprocessor available in otel mode #4969

[mergify]

This pull request does not have a backport label. Could you fix it @andrzej-stencel? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

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

NOTE: backport-skip has been added to this pull request.

[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 otel-add-elastic-infra-metrics-processor upstream/otel-add-elastic-infra-metrics-processor
git merge upstream/main
git push upstream otel-add-elastic-infra-metrics-processor

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube