[chore] Move service/telemetry implementation

[axw]

Description

Move the telemetry implementation from service/telemetry to service/telemetry/otelconftelemetry, with the exception of the Settings type which is intended to remain in the service/telemetry package permanently. The goal here is to separate the interface (which is to be defined in a followup) and implementation, so multiple implementations can exist.

This move is in preparation for creating a new Telemetry and Factory interface, similar to pipeline components. In the end, the implementation (e.g. otelconftelemetry) will be completely self contained, providing a NewFactory function to obtain a factory that can be used to construct a Telemetry implementation.

The next steps after this PR would be:

1. Update https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/7bf3615b56d443c522d5b5591ce53d5fe43b8b47/cmd/opampsupervisor/supervisor/config/config.go#L25 to use otelconftelemetry. Eventually the opampsupervisor should probably use the Factory & Telemetry, but that can be done later on.
2. Create the Factory and Telemetry interface in service/telemetry, and update otelconftelemetry to implement it, encapsulating the creation of the SDK & SDK resource. We would continue directly constructing the otelconftelemetry factory to keep the change contained. At this stage we could close Move telemetry initialization logic to service/telemetry #8170.
3. Update otelcol and service packages to inject the telemetry factory & default config into the service's settings and default config, and remove direct references to otelconftelemetry in the service package. At this stage we could close Allow overriding telemetry providers #4970.

Link to tracking issue

Part of #4970

Testing

N/A, non-functional change.

Documentation

N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.23%. Comparing base (e8497df) to head (9b1b8d8).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13560      +/-   ##
==========================================
- Coverage   92.24%   92.23%   -0.02%     
==========================================
  Files         605      605              
  Lines       31909    31911       +2     
==========================================
- Hits        29435    29433       -2     
- Misses       1952     1955       +3     
- Partials      522      523       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[mx-psi]

Can we add a reference to an issue tracking this here and in the other TODO?

I would also add a proper godoc comment that says "this is experimental and will change soon use at your own risk"

[axw]

Done. I've linked to #4970, and added some NOTEs to warn against use in the mean time.