perf: improve org and org domain creation (#10232)

# Which Problems Are Solved

When an organization domain is verified, e.g. also when creating a new
organization (incl. generated domain), existing usernames are checked if
the domain has been claimed.
The query was not optimized for instances with many users and
organizations.

# How the Problems Are Solved

- Replace the query, which was searching over the users projection with
(computed loginnames) with a dedicated query checking the loginnames
projection directly.
-  All occurrences have been updated to use the new query.

# Additional Changes

None

# Additional Context

- reported through support
- requires backport to v3.x

(cherry picked from commit fefeaea56a)

internal/query/user_claimed_user_ids.sql

@@ -0,0 +1,13 @@
+SELECT u.id
+FROM projections.login_names3_users u
+    LEFT JOIN projections.login_names3_policies p_custom
+        ON  u.instance_id = p_custom.instance_id
+            AND p_custom.instance_id = $1
+            AND p_custom.resource_owner = u.resource_owner
+    JOIN projections.login_names3_policies p_default
+        ON  u.instance_id = p_default.instance_id
+            AND p_default.instance_id = $1 AND p_default.is_default IS TRUE
+WHERE u.instance_id = $1
+    AND COALESCE(p_custom.must_be_domain, p_default.must_be_domain) = false
+    AND u.user_name_lower like $2
+    AND u.resource_owner <> $3;