[ENHANCEMENT] Lock app immediately

[michaeltroger]

Is your feature request related to a problem? Please describe.
When authentication is enabled, then the app is only locked after the timeout (5min), when the app is force closed or when the app is manually locked via the "lock" button. Depending on your usage behavior you might would expect the app to lock immediately when leaving the app. This was originally requested by a user via Google Play Review.

Describe the solution you'd like
To have a new, optional setting to lock the app immediately if authentication is enabled and you leave the app.

Describe alternatives you've considered
x

Additional context
Keep in mind that some features can become contradicting e.g. "app over lock screen", "authentication", "immediately lock screen"