[8.19](backport #48407) test: add benchmark for OTel Beat processor

[mergify]

Proposed commit message

Adds a microbenchmark to measure the overhead of the OTel Beat processor.

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. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• [ ] I have added an entry in ./changelog/fragments using the changelog tool.

How to test this PR locally

cd x-pack/otel/processor/beatprocessor/
go test -benchmem . -run ^$ -bench=BenchmarkBeatProcessor

Results from my machine:

goos: darwin
goarch: arm64
pkg: github.com/elastic/beats/v7/x-pack/otel/processor/beatprocessor
cpu: Apple M2 Pro
BenchmarkBeatProcessor/empty_log_record/0_logs-12               338138461                3.519 ns/op           0 B/op          0 allocs/op
BenchmarkBeatProcessor/empty_log_record/1_logs-12               10082673               116.0 ns/op           208 B/op          4 allocs/op
BenchmarkBeatProcessor/empty_log_record/1000_logs-12               10000            111746 ns/op          208001 B/op       4000 allocs/op
BenchmarkBeatProcessor/message/1_logs-12                         2766692               429.6 ns/op           848 B/op          9 allocs/op
BenchmarkBeatProcessor/message/1000_logs-12                         2744            431760 ns/op          848006 B/op       9000 allocs/op
BenchmarkBeatProcessor/Kubernetes_log/1_logs-12                  2112459               565.0 ns/op           976 B/op         13 allocs/op
BenchmarkBeatProcessor/Kubernetes_log/1000_logs-12                  2005            578497 ns/op          976006 B/op      13000 allocs/op
BenchmarkBeatProcessor/Nginx_access_log/1_logs-12                 628468              1814 ns/op            2200 B/op         35 allocs/op
BenchmarkBeatProcessor/Nginx_access_log/1000_logs-12                 637           1847566 ns/op         2200017 B/op      35000 allocs/op
PASS
ok      github.com/elastic/beats/v7/x-pack/otel/processor/beatprocessor 11.602s

---

This is an automatic backport of pull request #48407 done by [Mergify](https://mergify.com).

[elasticmachine]

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

[github-actions]

🤖 GitHub comments

Just comment with:

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