This patch fixes the documentation structure for:
- Move Overview from UserGuide to top page
- Move OAuth2.0, OpenID and DB migration tool documentation
to AdminGuide
- Move Policy documentation to ConfigurationGuide
- Add `Tools` to Reference
- Move FaultNotification documentation to `Management Driver`
- Move Prometheus documentation to `Prometheus Plugin`
- Add link to command list and ConfigurationGuide to AdminGuide
- Add `VNF Package` to `v1/v2 Tacker Use Cases`
and move VNF Package sample documentation to `VNF Package`
- Move Coordinate API client script documentation
to `Change Current VNF Package`
Change-Id: Ie8a1df67266d90e3960060d922786d22352619d6
9e4d92feac