Add bluetooth discoverable footer preference in connected devices page

* Dynamicly add preference in controller
* Add test cases for DiscoverableFooterPreferenceController

Bug: 79294219
Test: make -j50 RunSettingsRoboTests
Change-Id: Id4c1e86c9a0a0cd69d8106a18f2cf4a0fa31782b
Merged-In: Id4c1e86c9a0a0cd69d8106a18f2cf4a0fa31782b
5 files changed