Add intent for entering communal settings

This allows other apps to link to communal settings.

Fixes: 276742740
Test: adb shell am start -a android.settings.COMMUNAL_SETTINGS
Test: switched to secondary user, attempted to launch using command
above. Verified it didn't work

Change-Id: I5e845ecba58d8443d41aeea95bc6068a0041cac8