feat: LDAP User management

LDAP will be used as default if no other auth form is enabled.
LDAP now will work with ENABLE_LOGIN_FORM = false.
Fixed exception "User does not match the record."
Now LDAP login is case insensitive.
Integrated with onboarding feature.

backend/open_webui/apps/webui/models/auths.py

@@ -64,6 +64,11 @@ class SigninForm(BaseModel):
     password: str
 
 
+class LdapForm(BaseModel):
+    user: str
+    password: str
+
+
 class ProfileImageUrlForm(BaseModel):
     profile_image_url: str