4.1: Deprecate two OAuth 2 settings

[MarcialRosales]

Implements these two features:

• https://github.com/rabbitmq/rabbitmq-server/issues/12239
• https://github.com/rabbitmq/rabbitmq-server/issues/12237

Only for 4.1.x

This PR should only be merged after this PR has been merged. and this PR has been rebased too.

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[michaelklishin]

@MarcialRosales same here, can you please resolve the conflicts?