Add root password change

[gizmo693]

Users should be able to override the master password in the config -> should proxy to the snap

[buggtb]

Along with the above where a user can change the config option and update the password on install we should randomise it:

We should add a command to change the admin password in the config block:

snap set openldap password=<top secret password>

Where the password is a 8-12 character password generated at random. You also need to write that password to a textfile in the /root folder.

• [x] Generate password
• [x] Add password code to charm
• [x] Write password to file
• [x] Update password on config change