[8.x] Translate otel metrics to libbeat monitoring (backport #15094)

[mergify]

Motivation/summary

use otel api to record metrics and export them to beats monitoring

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

• run apm-server
• send data
• go to index management and validate the monitoring index is there and monitoring data is inside it

Related issues

Related to #14488

---

This is an automatic backport of pull request #15094 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 378b60c has failed:

On branch mergify/bp/8.x/pr-15094
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit 378b60c2.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   internal/agentcfg/elasticsearch.go
	modified:   internal/agentcfg/elasticsearch_test.go
	modified:   internal/beatcmd/reloader.go
	modified:   internal/beater/api/config/agent/handler.go
	modified:   internal/beater/api/intake/handler.go
	modified:   internal/beater/api/intake/handler_test.go
	modified:   internal/beater/api/mux.go
	modified:   internal/beater/api/mux_config_agent_test.go
	modified:   internal/beater/api/mux_intake_backend_test.go
	modified:   internal/beater/api/mux_intake_rum_test.go
	modified:   internal/beater/api/mux_root_test.go
	modified:   internal/beater/api/mux_test.go
	modified:   internal/beater/api/root/handler.go
	modified:   internal/beater/interceptors/metrics.go
	modified:   internal/beater/interceptors/metrics_test.go
	modified:   internal/beater/middleware/monitoring_middleware.go
	modified:   internal/beater/middleware/monitoring_middleware_test.go
	deleted:    internal/beater/monitoringtest/monitoring.go
	modified:   internal/beater/monitoringtest/opentelemetry.go
	deleted:    internal/beater/otlp/common.go
	modified:   internal/beater/otlp/grpc.go
	modified:   internal/beater/otlp/grpc_test.go
	modified:   internal/beater/otlp/http.go
	modified:   internal/beater/otlp/http_test.go
	modified:   internal/beater/request/result.go
	modified:   internal/beater/request/result_test.go
	modified:   internal/beater/tracing.go
	modified:   internal/model/modelprocessor/eventcounter.go
	modified:   internal/model/modelprocessor/eventcounter_test.go
	deleted:    internal/processor/stream/result.go
	deleted:    internal/processor/stream/result_test.go
	modified:   systemtest/otlp_test.go
	modified:   x-pack/apm-server/main.go
	modified:   x-pack/apm-server/main_test.go
	modified:   x-pack/apm-server/sampling/config.go
	modified:   x-pack/apm-server/sampling/groups.go
	modified:   x-pack/apm-server/sampling/groups_test.go
	modified:   x-pack/apm-server/sampling/processor.go
	modified:   x-pack/apm-server/sampling/processor_bench_test.go
	modified:   x-pack/apm-server/sampling/processor_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   internal/beatcmd/beat.go
	both modified:   internal/beater/beater.go
	both modified:   internal/beater/server.go
	both modified:   internal/beater/server_test.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[carsonip]

@kruskall why is this closed? Is it because we do not intend to backport this to 8.x?

[mergify]

This pull request is now in conflicts. Could you fix it @mergify[bot]? 🙏
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 mergify/bp/8.x/pr-15094 upstream/mergify/bp/8.x/pr-15094
git merge upstream/8.x
git push upstream mergify/bp/8.x/pr-15094