Password change

[tsmethurst]

This PR adds the command gotosocial admin account password for changing the password of an account.

NAME:
   gotosocial admin account password - set a new password for the given account

USAGE:
   gotosocial admin account password [command options] [arguments...]

OPTIONS:
   --username value  the username to create/delete/etc
   --password value  the password to set for this account
   --help, -h        show help (default: false)

It also adds some initial documentation for the various CLI commands, and some usage examples.