Add ClientRegistration.withClientRegistration(ClientRegistration)

[jzheaux]

Given that a ClientRegistration has numerous possible inputs, it may be handy to take an existing ClientRegistration and build a new one from it, say, to just change a single value.

ClientRegistration clientRegistration = this.repository.findByRegistrationId(id);
ClientRegistration updated = ClientRegistration.withClientRegistration(clientRegistration)
        .clientSecret(updatedSecret).build();