Add project_tags identity feature flag

This PS adds the project_tags identity feature flag which allows
identity v3 project tags API functionality to be enabled for
releases after Pike. Once Pike is no longer supported in Tempest
this feature flag can be removed.

Needed-By: Iec6b34c10ea1bd7103720c773b48ce130643115d
Needed-By: Iad6b3a88639bb4a0dc3aea5af2ba0162dfa19f96
Change-Id: Ibaec1df79c9ac69c65cf5075c3519092bc609546
1 file changed