bas: add Battery service profile support

This profile provides the battery level characteristic
of the BLE device.

Settings.Global."settings_bluetooth_battery" or
"sys.fflag.override.settings_bluetooth_battery" should be set
to enable the feature. (or the ProfileService doesn't start)

Bug: 193631822
Tag: #feature
Test: atest BatteryStateMachineTest BatteryServiceTest
	DatabaseManagerTest AdapterServiceTest
 && manually with BLE keyboard as well
Change-Id: I5459218a3362e97f37128aa6bdf286ccbdbc8761