Improve adding keycloak plugins

- [ ] Copy all plugins folder in the accounts Dockerfile like `COPY plugins/ /opt/jboss/keycloak/standalone/deployments/`
- [ ] Add an option to enable plugins from the account's values.yaml file instead of overriding the full realm.json file.

application/accounts/values.yaml
```yaml
plugins:
- metacell-admin-event-listener
- my-plugin
```

Start with the accounts Dockerfile and application/accounts/values.yaml, then inspect the plugins folder and the current realm.json handling. The work is done when the plugins folder is copied into the Keycloak deployments path and plugins can be enabled through values.yaml without overriding the full realm.json file.

Written by the indexing model from the issue text.