* changed ExistingPeriodicWorkPolicy to KEEP for deadman check task to stop notification loop on every app open

Signed-off-by: Kolya Opahle <k.opahle@sap.com>

* fixed tests

Signed-off-by: Kolya Opahle <k.opahle@sap.com>

* Added info text to the schedulePeriodic doc ...

... to explain the change to ExistingPeriodicWorkPolicy

* Fixed linting

Co-authored-by: Ralf Gehrer <ralfgehrer@users.noreply.github.com>
Co-authored-by: harambasicluka <64483219+harambasicluka@users.noreply.github.com>