Implemented functionalities to allow multiple LDAP configs

[Riccardo-Maffei]

Hey there! I had to use multiple configurations for my Django Application and i was already using this package, so I tried to implement the functionality myself. I've tested it a bit and up until now it seems to be working, but documentation is still mostly missing.

With this implementation, the user would need to implement a subclass of the LDAP Backend class

class MyBackend(LDAPBackend):
    PREFIX = 'MY_PREFIX_'

and add the required data to settings.py. If the value of a specific setting does not change across LDAP Backends, the user can stick to the default name (no prefix). Thanks to this feature, the new code is entirely compatible with programs that use previous versions of the python3-ldap package.

AUTHENTICATION_BACKENDS = [
    'custom_backends.MyBackend',
    'django_python3_ldap.auth.LDAPBackend',
    'django.contrib.auth.backends.ModelBackend',
]

# Uses different configs for each Backend
LDAP_AUTH_URL = 'ldap://my_ldap:1234'
MY_PREFIX_LDAP_AUTH_URL = f'ldap://my_other_ldap:4321'

# Uses same config for both Backends
LDAP_AUTH_OBJECT_CLASS = '*'

What do you think about it?