Add background support directly to CAMS

[bardram]

Right now, background support in CAMS relies on sampling location data from the carp_context_package. We should support this natively in CAMS, using e.g. the flutter_background plugin.

[bardram]

Note that the type of foreground service(s) needs to be declared in the Manifest file and later specified when submitting an app to the Google Play Console - see

• https://developer.android.com/about/versions/14/changes/fgs-types-required
• https://developer.android.com/develop/background-work/services/fgs/service-types

[iarata]

Found this https://www.researchandcare.org/resources/background-health-research-task-entitlement/ from ResearchKit for iOS.
Perhaps a flutter wrapper for ResearchKit (now carp-research-flutter)