[sso] add support for ConfigMap, so user can import custom realm.json

[pschiffe]

When trying to deploy SSO application to OpenShift automatically (e.g. with ansible), it's currently not possible to provide custom realm configuration which would be imported to the newly created instance. This could be done by supporting ConfigMaps, where user can provide custom realm.json file, which in the end could be automatically imported to the SSO during startup.

I did a POC for this use case, which can be found here: https://github.com/pschiffe/keycloak-demo Modified sso70-https.json template file contains new SSO_IMPORT_FILE parameter and variable and a sso-realm-volume with content of sso-realm ConfigMap.

[ecoupal]

+1

[rcernich]

@iankko FYI.