Feature/ui dashboard setting

* Dashboard endpoints [Namespace aware]
* User Settings endpoints

The PR does not contain (will be added in future):
* ACLClient integration (Dashboard Read/Write access check)
* Namespace deletion hook --> Delete all dashboards belonging to that namespace when it is deleted.
yeah - it should not be a part of back-end API. The service should not care about what is stores, unless there's different handling on the back-end for different types. Which is not the case