Fix some external_id issues

- Do not update `externalId` on group updates
   Groups are only updated via the web-vault currently, and those do not
   send the `externalId` value, and thus we need to prevent updating it.
 - Refactored some other ExternalId functions
 - Prevent empty `externalId` on `Collections`
 - Return `externalId` for users

Fixes #3685

src/db/models/organization.rs

@@ -434,6 +434,7 @@ impl UserOrganization {
             "UserId": self.user_uuid,
             "Name": user.name,
             "Email": user.email,
+            "ExternalId": user.external_id,
             "Groups": groups,
             "Collections": collections,
 
@@ -441,7 +442,7 @@ impl UserOrganization {
             "Type": self.atype,
             "AccessAll": self.access_all,
             "TwoFactorEnabled": twofactor_enabled,
-            "ResetPasswordEnrolled":self.reset_password_key.is_some(),
+            "ResetPasswordEnrolled": self.reset_password_key.is_some(),
 
             "Object": "organizationUserUserDetails",
         })