Add check for LDAP group membership (#10869)

This is a port of gogs/gogs#4398

The only changes made by myself are:

Add locales
Add some JS to the UI
Otherwise all code credit goes to @aboron

Resolves #10829

Signed-off-by: jolheiser <john.olheiser@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>

modules/auth/ldap/README.md

@@ -103,3 +103,21 @@ share the following fields:
       matching parameter will be substituted with the user's username.
     * Example: (&(objectClass=posixAccount)(cn=%s))
     * Example: (&(objectClass=posixAccount)(uid=%s))
+
+**Verify group membership in LDAP** uses the following fields:
+
+* Group Search Base (optional)
+    * The LDAP DN used for groups.
+    * Example: ou=group,dc=mydomain,dc=com
+
+* Group Name Filter (optional)
+    * An LDAP filter declaring how to find valid groups in the above DN.
+    * Example: (|(cn=gitea_users)(cn=admins))
+
+* User Attribute in Group (optional)
+    * Which user LDAP attribute is listed in the group.
+    * Example: uid
+
+* Group Attribute for User (optional)
+    * Which group LDAP attribute contains an array above user attribute names.
+    * Example: memberUid