Add multiple env variables to provide an easy way to set password policies for new users

[Y0ngg4n]

This PR adds the following environment variables:

- MIN_PASSWORD_LENGTH=8 # Minimum password length required for new users (default: 8)
- MAX_PASSWORD_LENGTH=20 # Maximum password length for new users (default: 20)
- MIN_PASSWORD_UPPERCASE=1 # Minimum password chars that are uppercase (default: 1)
- MIN_PASSWORD_NUMBERS=1 # Minimum password chars that are numbers (default: 1)
- MIN_PASSWORD_SPECIAL=0 # Minimum password chars that are special (default: 0)   

with this environment variables the admin can define the password policy via environment variables to provide an easy way to set minimum requirements for the passwords for new users.