Add missing @Consumes annotation to UserResource.addFederatedIdentity

Closes #41188

Signed-off-by: Stefan Guilhen <sguilhen@redhat.com>

services/src/main/java/org/keycloak/services/resources/admin/UserResource.java

@@ -511,6 +511,7 @@ public class UserResource {
     @Path("federated-identity/{provider}")
     @POST
     @NoCache
+    @Consumes(MediaType.APPLICATION_JSON)
     @Tag(name = KeycloakOpenAPI.Admin.Tags.USERS)
     @Operation(summary = "Add a social login provider to the user")
     @APIResponses(value = {