Implemented tracing configs

[denniskniep]

Summary

Implements the tracing configs in the Pomerium CRD

Checklist

• reference any related issues
• updated docs
• updated unit tests
• updated UPGRADING.md
• add appropriate tag (improvement / bug / etc)
• ready for review

[CLAassistant]

All committers have signed the CLA.

[wasaga]

my preference would be to keep CRD structured rather then a flat list of parameters, similar to other options:

tracing:
  datadog:
    address: xxxxxxx

or

tracing:
  jaeger:
    collectorEndpoint: xxxx

and

• implicitly setting the provider based on which key is used
• adding a validation rule that two providers may not be defined simultaneously

imagine in future we would have OTEL export for example that may have a whole bunch of parameters and it would be nice to group them somewhere under

tracing:
  otel:

this spec is used to auto-generate reference documentation with topmost level keys becoming sections: https://www.pomerium.com/docs/deploying/k8s/reference

[eadwu]

Is it still not possible to configure tracing with Pomerium using this? It seems like setting it via environment variables doesn't work either (i.e. TRACING_PROVIDER).