Allow appending custom jwt token data to the request

[parallels999]

Currently, it's easy to implement the convertToJWT method in the AccessTokenEntityInterface implementation to add data to the JWT. However, i don't see any solution, except creating a new implementation of BearerTokenValidator, to add additional attributes from the token, to the returning ServerRequestInterface object.

I think this PR can provide a way to simply override the BearerTokenValidator::appendAttributesFromClaims() method and pass the custom BearerTokenValidator instance to the ResourceServer instance.

Complement of #1328
Alternative of #851

[parallels999]

Closed because #1328 added the same now