Get communal widget allowlist from config.xml

Defines the component names for the widget allowlist in config
xml and stores the metadata in CommunalWidgetRepository, which
will later be needed when creating the db.
The metadata will be used to create the widget inventory flow.

Bug: b/303844599
Test: atest CommunalWidgetRepositoryImplTest
Change-Id: I40e931be85dd0459b3ad092668eb64f8392ca840