Docs: Add documentation on policy feature flags

This is to add documentation on policy feature flags, recently
introduced in [0].

[0] Ia0d9847908a8e723446c16465d68cd7f622c04cc

Depends-On: Ia47132fa596918e58f21ba9810c2c28ddcf0d584
Change-Id: I3e630c535074e3a9ce8e9b07a1909984d70cef12
4 files changed