Add a live timer countdown to the notification for when it'll auto-lock

**Is your feature request related to a problem? Please describe.**
It'd be great to have a persistent reminder of when the database will lock itself.

**Describe the solution you'd like**
Some crypto wallet apps show a live, second-by-second countdown of when the wallet will lock itself. It'd be great if KeePassDX could do the same!

**Describe alternatives you've considered**
N/A

**Additional context**
N/A

No files or tests are named in the issue. Start by tracing the auto-lock timing and the Android notification that reminds users about it; done means the notification shows a live, second-by-second countdown until the database locks.

Written by the indexing model from the issue text.