[Feature] Support custom LDAP server

[adonal1]

📄 Description

I'd like to see instructions on how to use an existing LDAP server instead of Geti hosting its own. Basically, you would configure LDAP settings with Helm and it would be able to use authenticate against an existing LDAP server. This could either use OpenLDAP as a proxy or use the external LDAP server directly.

🎯 Objective

Users can login with their Active Directory credentials instead of having a separate login. Then admin and contributor access can be restricted to a group.