saving a container .kdbx inside a protected folder

**Is your feature request related to a problem? Please describe.**
now it is possible to store the container .kdbx only on public flash memory. any program can read the contents .kdbx of any folder find a container and steal it. I know that the container is encrypted. but you can still hack the container.

**Describe the solution you'd like**
need to store inside a folder: **/data/data/com.kunzisoft.keepass.libre**
only the program itself and the system have access to this folder.
third-party programs will not be able to steal data.
to get this container later, you can add an item in the menu: save a copy of the container or export.

Start by locating the existing container save/open flows and the menu actions for saving or exporting a .kdbx file. Determine how Android app-private storage at /data/data/com.kunzisoft.keepass.libre can be used while retaining an explicit export path. Done means containers can be stored privately and users can still save a copy or export one.

Written by the indexing model from the issue text.