docs: New "app compatibility with managed profiles" doc

Doc on steps app developers can take to make sure their apps will
behave properly in a managed-profile environment. Doesn't talk about
unreleased features, this is intended to go live on DAC in December.

See first comment for doc stage location.

Change-Id: I82e17e6085f732096e2aff40fea52d3ddafcf3ee