feat(exceptions): Add SpinnakerRetrofitErrorHandler and replace RetrofitError catch blocks

[alice485]

This pull request registers SpinnakerRetrofitErrorHandler with each Retrofit.RestAdapter and replaces each RetrofitError catch block with a catch-block using SpinnakerServerException or the appropriate subclass.

This change does not alter any of this service's behavior, it merely allows error messages to be surfaced even when the error was thrown in a microservice more than one network call from the service in which the request originated.

This is part of an effort to consume SpinnakerRetrofitErrorHandler in each Spinnaker microservice, as detailed in spinnaker/spinnaker#5473

[spinnakerbot]

The following commits need their title changed:

• c75541c: add spinnakerRetrofitErrorHandler and replace RetrofitError catch blocks with SpinnakerServerException, etc

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