feat: add `enablePasswordDB` charm configuration option to enable/disable static password login

[DnPlas]

This change addresses #76, allowing enablePasswordDB to be disabled. Changes are:

• The enablePasswordDB flag is now configurable
• Updated the unit test to cover the new configuration

NOTE: this is a clone of #122 to be able to run the CI and test this addition. Thanks to @alhama7a for the contribution.