OIDCClientConfiguration#getClaimsRequest() won't return configured claims

Since e8c6481, we use com.nimbusds.openid.connect.sdk.OIDCClaimsRequest to transport OIDC Claims in the OIDCClientConfiguration#getClaimsRequest instead of the previously used com.nimbusds.openid.connect.sdk.ClaimsRequest.

One difference between these two classes is that OIDCClaimsRequest is immutable, and thus we need to instantiate a new object of this class every time a change is needed.