apk signature checking added for cleanapk

Description

Apk signature checking is implemented for apps from cleanapk.
Some logical error is fixed found during unit test
Some unit tests are added

Issue(s)

backlog/-/issues/5761
backlog/-/issues/5916

Test environment

Gradle build against 5761-match_fdroid_signature branch, install the apk into the device

Test procedures

Technical details

Screenshots

Check list

• Self review
• Test procedure explained
• Tested on fresh install
• Tested applied as an update
• License
• Internal documentation
• User documentation