Update 2.9 release notes to mention fixes from 2.8.6

The 2.9 release will include the fixes done in 2.8.6.

Change-Id: I78269f691a335551ba5821a68c3d9afbeeafc167
Docs: changes /index endpoint requires administrateServer capability

The documentation of the /index REST API endpoint was added
with commit 4e38b97171ed4851395655435ab88d7d93da6bee but omitted
to mention that the caller must be a member of a group that is
granted the administrateServer capability.

Change-Id: Ic71dcd887e2f7ec3ea3194102aa8cd4f6c539398