Add overlay for Instant Apps Settings whitelists

Some non-platform settings may need to be exposed to Instant Apps. To
enable that config_allowed{Global,System,Secure}InstantAppSettings has
been added to supplement the hardcoded platform whitelist in Settings.

Bug: 37765840
Test: Run instant app from b/37765840
Change-Id: Ie1e9c645068db1d3d961d2f597c6ee2dfa158843