enable event-metrics-user-enabled in Keycloak benchmark deployments

[kami619]

Tasks

Beta Give feedback

1. update the keycloak.yaml
2. update the docs
3. verify different dimensions for realm, idp, clientId
4. make the dimension options configurable
5. run performance tests to see if there an overhead with and without the user event metrics

[ahus1]

With the large number of clients we're running here, the clientId dimension should probably skipped. We also don't use IDPs here. Therefore IMHO the "verify different dimensions for realm, idp, clientId" could be minimal. Also for the "make the dimension options configurable" I'm not sure if that is needed in our helm charts (except if you have a scenario where need it)