suppress instrumentation: move to api + generic context key

[SylvainJuge]

With #5918, the suppress_internal_exporter_instrumentation context key was introduced as a way to help identify the HTTP calls made by the OTLP exporter from the ones made by the application.

The name of the context key and the location of the related InstrumentationUtil class in the exporter make it exporter-only, which somehow blocks reusing it more broadly.

Other implementations seem to favor a more generic naming, so it seems reasonable to change:

• python: suppress_instrumentation and suppress_http_instrumentation (definitions)
• C# : otel.suppress_instrumentation (definition)

My goal here is to help unblock this PR open-telemetry/opentelemetry-java-contrib#1061 : okhttp is implicitly ignored for now due to classloader, but switching to internal JDK HTTP client means we need to have explicit exclusion

Also, this should help ensure that other internal HTTP clients usages like GCP/AWS (and maybe soon Azure too) cloud resource attributes providers are consistently excluded from tracing.

There has already been an issue opened to attempt adding this officially to the spec/semantic conventions in the past (open-telemetry/opentelemetry-specification#530) but there hasn't been any progress in a while, so we can conclude that there isn't any strong need to align this across platforms for now, this could however be a welcome later improvement.

[SylvainJuge]

[for reviewer] keeping this class allows to keep instrumentation agent compatible as it currently relies on it, switching to the new class location is the next step in the instrumentation agent once this has been merged and released.

[LikeTheSalad]

Moving the tool outside of the exporters module should also help avoid using reflection here!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.61%. Comparing base (20bcd75) to head (5b82090).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6546      +/-   ##
============================================
+ Coverage     90.59%   90.61%   +0.01%     
- Complexity     6255     6257       +2     
============================================
  Files           689      690       +1     
  Lines         18698    18701       +3     
  Branches       1843     1843              
============================================
+ Hits          16940    16945       +5     
  Misses         1201     1201              
+ Partials        557      555       -2     

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[jack-berg]

Just the one comment on location, but I support this.