Require that both RS256 and ES256 must be supported if the signature algorithm is not configured

[sberyozkin]

This PR is meant to align a situation with a non configured signature algorithm is managed with how it is done for the unconfigured decryption algorithm.

If a decryption algorithm is not configured, both RSA-OAEP and RSA-OAEP-256 encryped tokens must be accepted.

Now, similarly, if a signature algorithm is not configured, both RS256 and ES256 signed tokens must be accepted.

The end goal is to let an MP JWT Bridge JwtAuthenticationMechanismDefinition offer a consistent List representation for both signature and encryption properties

CC @ayoho @jimmy1wu

[sberyozkin]

I'll support ii with TCK tests once it is agreed via approvals

[sberyozkin]

There is a real lot of assertions in TCK tests expecting RS256 by default

[sberyozkin]

That said, the spec does not require anywhere that the signature algorithm must be injected as a string and not as a set of strings, so I may as well tweak TCK tests to expect a List<String> injection for the signature alg configuration property.