Add smallrye.jwt.new-token.override-matching-claims property

[sberyozkin]

Fixes #420

This PR supports making the new-token.issuer and new-token.audience override the existing claims, such that, for example, in quarkus-oidc-token-propagation I can code:

@Inject JsonWebToken jwt;

String newJwt = Jwt.claims(jwt).sign();

and doc that the users - if they need this feature, should only configure the new signing key, and/or issuer and audience
etc.

Totally isolated to jwt-build

[MikeEdgar]

Looks good!

[sberyozkin]

@MikeEdgar thanks, I think a single approval is enough for this update, CC @radcortez Roberto - I'll CC you in my Quarkus PR :-)

[sberyozkin]

Just updated the branch