Bugfix: no stups token bean if not needed

[ePaul]

When the application already supplies a NakadiPublishingClient or NakadiClient bean, we don't need our own authentication setup.

This was already meant to be skipped, but I guess we misunderstood how nested configuration classes work – they don't inherit their outer classes' conditions.

As an effect, even when one of these beans is already there, a new StupsTokenComponent bean was created (and the build failed if that was not possible e.g. due to missing configuration variables).

• This adds a test which checks that the StupsTokenComponent bean is not created when we got the MockPublishingClient bean. (Fails if just running the first commit.)

• We then make the creation of the StupsTokenComponent dependent on missing both beans.

  As an effect, when running the tests we don't get all the error messages about missing CREDENTIALS_DIR environment variables anymore.

• As a bonus, we also add an AccessTokenProvider @MockBean to NakadiClientEncodingIT (which doesn't have a NakadiPublishingClient) to avoid getting the error messages about CREDENTIALS_DIR here.

[ePaul]

:+1:

[fbrns]

👍