OAuth 2: support scope aliases in rabbitmq.conf

[MarcialRosales]

Proposed Changes

Implements feature request #12210

Types of Changes

What types of changes does your code introduce to this project?
Put an x in the boxes that apply

• Bug fix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
• Documentation improvements (corrections, new content, etc)
• Cosmetic change (whitespace, formatting, etc)
• Build system and/or CI

This PR is accompanied by docs PR rabbitmq/rabbitmq-website#2091

[michaelklishin]

I can reproduce the failures locally on both Erlang 26.2 and 27.1:

rabbit_oauth2_schema_SUITE > test_with_one_oauth_provider
    #1. {error,
            {{badmatch,#{<<"keycloak">> => [{issuer,"https://rabbit"}]}},
             [{rabbit_oauth2_schema_SUITE,test_with_one_oauth_provider,1,
                  [{file,"rabbit_oauth2_schema_SUITE.erl"},{line,106}]},
              {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1793}]},
              {test_server,run_test_case_eval1,6,
                  [{file,"test_server.erl"},{line,1302}]},
              {test_server,run_test_case_eval,9,
                  [{file,"test_server.erl"},{line,1234}]}]}}

rabbit_oauth2_schema_SUITE > test_with_many_oauth_providers
    #1. {error,
            {{badmatch,
                 #{<<"keycloak">> => [{issuer,"https://keycloak"}],
                   <<"uaa">> =>
                       [{issuer,"https://uaa"},
                        {discovery_endpoint_path,"/some-path"}]}},
             [{rabbit_oauth2_schema_SUITE,test_with_many_oauth_providers,1,
                  [{file,"rabbit_oauth2_schema_SUITE.erl"},{line,125}]},
              {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1793}]},
              {test_server,run_test_case_eval1,6,
                  [{file,"test_server.erl"},{line,1302}]},
              {test_server,run_test_case_eval,9,
                  [{file,"test_server.erl"},{line,1234}]}]}}

rabbit_oauth2_schema_SUITE > test_oauth_providers_signing_keys
    #1. {error,
            {{badmatch,
                 #{<<"keycloak">> =>
                       [{issuer,"https://keycloak"},
                        {signing_keys,
                            #{<<"1">> => {pem,<<"I'm not a certificate">>},
                              <<"2">> =>
                                  {pem,<<"I'm not a certificate">>}}}]}},
             [{rabbit_oauth2_schema_SUITE,test_oauth_providers_signing_keys,
                  1,
                  [{file,"rabbit_oauth2_schema_SUITE.erl"},{line,277}]},
              {test_server,ts_tc,3,[{file,"test_server.erl"},{line,1793}]},
              {test_server,run_test_case_eval1,6,
                  [{file,"test_server.erl"},{line,1302}]},
              {test_server,run_test_case_eval,9,
                  [{file,"test_server.erl"},{line,1234}]}]}}
                  ```

[michaelklishin]

The forced push was a rebase on top of main to get #12500.