Add a primary action to slices from keyguard slice provider

We'll be enforcing requiring a primary action on slices.
There isn't a clear action that makes sense for these
slices... which is unfortunate but add a dummy one for now.

Test: atest KeyguardSliceProviderTest
Bug: 77855834
Change-Id: Ic37f9a8eba463654b3b2b93c1df9cb97d6d688a2