Collect some of the `trace_api.*` metrics in the trace flusher

[iamluc]

What does this PR do?

This PR collects some of the trace_api.* internal metrics in the trace flusher. These metrics are then sent by the "self telemetry" worker of the sidecar.

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

How to test the change?

Describe here in detail how the change can be validated.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 20.93863% with 219 lines in your changes are missing coverage. Please review.

Project coverage is 65.92%. Comparing base (9b531d5) to head (ef3c62e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
- Coverage   66.26%   65.92%   -0.34%     
==========================================
  Files         189      191       +2     
  Lines       23650    23767     +117     
==========================================
- Hits        15672    15669       -3     
- Misses       7978     8098     +120     

Components	Coverage Δ
crashtracker	19.34% <ø> (ø)
datadog-alloc	98.43% <ø> (ø)
data-pipeline	51.45% <0.00%> (ø)
data-pipeline-ffi	0.00% <ø> (ø)
ddcommon	81.52% <ø> (ø)
ddcommon-ffi	74.93% <ø> (ø)
ddtelemetry	53.72% <ø> (ø)
ipc	81.27% <ø> (ø)
profiling	77.52% <ø> (ø)
profiling-ffi	60.05% <ø> (ø)
serverless	0.00% <ø> (ø)
sidecar	31.02% <0.00%> (-0.74%)	:arrow_down:
sidecar-ffi	0.00% <ø> (ø)
spawn-worker	54.98% <ø> (ø)
trace-mini-agent	69.12% <66.66%> (ø)
trace-normalization	97.79% <ø> (ø)
trace-obfuscation	95.74% <ø> (ø)
trace-protobuf	25.64% <ø> (ø)
trace-utils	64.07% <28.42%> (-4.79%)	:arrow_down: