Replace internal model id with model name

[sschnabe]

At the moment Event (and AdminEvent) provides only internal database ids. In Grafana/Prometheus/... this must be mapped later to a human readable name. There should be an option to replace this database ids with names.

Todo:

• replace id with name:
  • Event.getRealmId() with RealmModel.getName()
  • Event.getClientId() with ClientModel.getClientId()
  • AdminEvent.getRealmId() with RealmModel.getName()
• add option KC_METRICS_EVENT_REPLACE_IDS with default true
• add option KC_METRICS_EVENT_REPLACE_IDS_CACHE_REALMS with default true, will cache realm names locally
• add option KC_METRICS_EVENT_REPLACE_IDS_CACHE_CLIENTS with default true, will cache clientIds locally

@wistefan any comments?