[FEATURE] Clean up internal Storage from unused key files

[grosshad]

I'm running a database with key file and as the primary storage of these is outside android / cloud so I monthly export / import the database and optional the key file from Keepass2Andriod internal data storage to normal data android storage to transfer / sync with the primary storage of those.files. After that I import those file back to Keepas2Andriod internal storage and delete the copies on normal Andriod Storage Based on my findings this causes every time the addition of at least the Keyfile as additional copy append with a numerical suffix to the internal Keepass2Andriod storage.

I'd like to have a option to see and delete all files that are on internal storage of Keepass2Andriod without rooting phone and using a file manager app so this function has to be launched in Keepass2Andriod security context