Adding API for displaying a DO/PO controlled secondary lock screen post initial system lock screen.

The new DPM API allows DP/POs to set whether the keyguard needs to show a secondary lockscreen after the primary locking mechanism is dismissed. If enabled, the keyguard will check for a service handling ACTION_BIND_SECONDARY_LOCKSCREEN_SERVICE and request the secondary lockscreen content from it.

Bug: 136085151
Test: atest FrameworksServicesTests:DevicePolicyManagerTest
Test: atest KeyguardUpdateMonitorTest
Test: atest AdminSecondaryLockScreenControllerTest
Change-Id: If82921b4fc2d78c0522a20ef91b48f9a93dd8b61