Improve pod logs related to Supervisor TLS certificate problems

[cfryanr]

This PR is meant to improve the situation described in #1393.

Because the certificate is selected inside a function which does not know the full details of the request, I was not able to log everything that I had hoped about each request. However, this PR is still an improvement and will hopefully be good enough.

This PR logs warnings that are visible at the default logging level when:

• there is any error reading the TLS certs from the Supervisor's default TLS cert Secret
• there is any error reading the TLS certs from the Secrets specified by FederationDomain.spec.tls.secretName
• there is any incoming request which will fail due to bad or missing user-provided TLS certs

The PR also changes the log level of some useful log lines for more verbose logging to make them available at the info log level, which is a level that should be safe to use on a production server for debugging. Previously, some of these useful log statements were at higher levels that are not safe or not convenient to use on production Supervisor servers.

All of these log messages include the SNI name from the request, to help the user see if their ingress is stripping SNI names from incoming requests.

Any changes aside from log statements are intended to be supporting refactors only, and are not intended to change any behavior at all. Please review for any possible accidental behavior changes.

Note that in the plog package, only plog.Error and plog.Warning are printed to the pod logs at the default log level. In order to see plog.Info messages, a user would need to choose to deploy the Supervisor with the info log level setting (or a higher level).

Release note:

Improvements to Supervisor pod logs to aid in debugging issues related to the Supervisor's user-provided TLS certificates.

[djpbessems]

After my initial struggles, this seems a very welcome improvement :)

[codecov]

Codecov Report

Merging #1662 (ce567c4) into main (3331171) will decrease coverage by 0.01%.
The diff coverage is 76.92%.

@@            Coverage Diff             @@
##             main    #1662      +/-   ##
==========================================
- Coverage   75.56%   75.55%   -0.01%     
==========================================
  Files         166      166              
  Lines       15139    15159      +20     
==========================================
+ Hits        11440    11454      +14     
- Misses       3398     3404       +6     
  Partials      301      301              

Files Changed	Coverage Δ
...l/controller/supervisorconfig/tls_cert_observer.go	89.41% <70.00%> (-6.18%)	⬇️
internal/oidc/provider/manager/manager.go	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes