Show characters typed in decrypt-backup

[nimrod-a]

This PR addresses the improvement request to show characters typed in decrypt-backup as asterisks (*), so that people can follow the characters they typed (#581)

The rich library currently used by MVT does seem to support this feature.

password = Prompt.ask("Enter backup password", password=True) # rich library

The builtin password support of the library leads to the characters being completely hidden.

Using the popular promt_toolkit instead:

prompt('Enter backup password: ', is_password=True) # 
# > Enter backup password: *******

When the is_password=True flag has been given, the input is replaced by asterisks (* characters).

The downside is that another library is used for password inputs.
However, this is a fairly simple solution for the issue.

Alternatively, one could also try and write a custom password prompt using the rich library.