Add management for configs

This PR enable the ability to manage configuration settings via adding a mongoose schema and Linz will convert this to a document and store it against linzconfigs collections.

To-do:
- [x] Linz to load config files and create documents in linzconfigs collection
- [ ] Add router control for accessing the list of config in the Admin UI
- [ ] Add navigation item to access the list of configs
- [ ] Editing capability for configs via Admin UI
- [ ] Overview display for config