switch to oslo-config-generator

the config generator has been moved to oslo.config. this patch
switches to use oslo.config and removes related deprecated code.

Change-Id: I9a22336142913d65da6299ea4092e170c9b2ff33
Add missing notification options to the documentation

Partial-Bug: 1380533
Change-Id: I5923e812de67f44b75a6f4719bc44403834a4136
Merge "switch to oslo-config-generator"
Merge "Add missing notification options to the documentation"