Configure a specific realm for application's gatekeeper

Currently, the namespace is used as the primary and only option to define the realm.
There are occasions when we want/need to use a different realm coming from external keycloak instance

https://github.com/MetaCell/cloud-harness/blob/0a5af041ba41739fdf649f1f1645a15a3b43c017/deployment-configuration/helm/templates/auto-gatekeepers.yaml#L13

So `.root.Release.Namespace` should be the default if `.app.accounts_realm` is not defined