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.

Depends-On: Ibaec1df79c9ac69c65cf5075c3519092bc609546
Change-Id: Iec6b34c10ea1bd7103720c773b48ce130643115d
1 file changed