Stop notification when App is at End of life (#897)

* Stop notification when at End of life

* Stopping background worker when user is tested positive and they submit the keys.

* Stop background services when diagnosis keys are submitted

* check added before starting backgrouns schedular

To prevent Backgrond services from starting again, a check has been added that checks if diagnosis keys are submitted already.

* tests modified based on code changes

Co-authored-by: Philipp Woessner <64482866+pwoessner@users.noreply.github.com>