Add option to disable sending telemetry to an Otel Collector

[p-j-smith]

Description

Fixes #646

• use the OTEL_SDK_DISABLED environment variable to determine whether telemetry should be disabled
• also disable telemetry if OTEL_SDK_DISABLED is False but OTEL_EXPORTER_OTLP_ENDPOINT is empty (otherwise we will still see errors in the logs)
• reuse the existing LoggerProvider created by opentelemetry, otherwise we see a warning in the logs: Overriding of current LoggerProvider is not allowed
• add tests to check the sdk can be disabled and the default logging provider reused
• update the docs

I've tested this on the GAE and it stops the error messages. If the sdk is enabled, we also need to make sure the service name of the endpoint is added to the no_proxy variable (or use docker.host.internal as the hostname for the endpoint)

Type of change

Please delete options accordingly to the description.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Suggested Checklist

• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have commented my code, particularly in hard-to-understand areas.
• I have passed on my local host device. (see further details at the CONTRIBUTING document)
• Make sure your branch is up-to-date with main branch. See CONTRIBUTING for a general example to syncronise your branch with the main branch.
• I have requested review to this PR.
• I have addressed and marked as resolved all the review comments in my PR.
• Finally, I have selected squash and merge

[codecov]

Codecov Report

❌ Patch coverage is 90.47619% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.52%. Comparing base (f4ad704) to head (2405278).

Files with missing lines	Patch %	Lines
pixl_core/src/core/telemetry.py	88.37%	5 Missing ⚠️
pixl_imaging/src/pixl_imaging/main.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #647      +/-   ##
==========================================
- Coverage   88.53%   88.52%   -0.02%     
==========================================
  Files          80       80              
  Lines        3813     3834      +21     
==========================================
+ Hits         3376     3394      +18     
- Misses        437      440       +3     

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[stefpiatek]

Thanks Paul, looking good