Use OTEL for metrics gathering (WIP)

[michel-laterman]

What is the problem this PR solves?

An onweek project to change fleet-server's metrics collection to use otel + the APM exporter as a bridge.

We are currently using a mixture of elastic-agent-libs and prometheus+an APM bridge.
This is a little messy and introduces unneeded dependencies and complexity.

OTEL metrics for the routes are now tagged with server.host and server.port attributes to allow us to determine when the internal/external API ports have issues.

A translation/export mechanism is provided so that we can continue to provide fleet-server metrics on the /stats endpoint for metricbeat collection/monitoring until we have determined how elastic-agent will monitor components with otel.

Note that it completely removes the option for the prometheus endpoint.
It also removes collecting the generic system/cpu/mem datasets.

TODO

• windows named pipe support
• beat.info population
• metrics server timeout values

How to test this PR locally

Start a server and ping 5066/stats to view the metricbeat stats endpoint.

Checklist

• 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

[michel-laterman]

This draft is unlikely to get worked on or merged anytime soon as we are still determining the otel roadmap

[mergify]

This pull request is now in conflicts. Could you fix it @michel-laterman? 🙏
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-metrics upstream/otel-metrics
git merge upstream/main
git push upstream otel-metrics

[mergify]

This pull request is now in conflicts. Could you fix it @michel-laterman? 🙏
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-metrics upstream/otel-metrics
git merge upstream/main
git push upstream otel-metrics