Update PM documentation for Keystore

Update the documentation about Hardware Keystore (KeyMint) in the
Package Manager.

Specifically, provide information about the new features added in
KeyMint v2 and KeyMint v3.

Bug: 304309651
Test: m docs , then manually look at the PackageManager doc
Change-Id: I9da0f94043e86749de9b654d7a19503ca6119023