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

internal/api/ui/login/login.go

@@ -178,19 +178,7 @@ func (l *Login) getClaimedUserIDsOfOrgDomain(ctx context.Context, orgName string
 	if err != nil {
 		return nil, err
 	}
-	loginName, err := query.NewUserPreferredLoginNameSearchQuery("@"+orgDomain, query.TextEndsWithIgnoreCase)
-	if err != nil {
-		return nil, err
-	}
-	users, err := l.query.SearchUsers(ctx, &query.UserSearchQueries{Queries: []query.SearchQuery{loginName}}, nil)
-	if err != nil {
-		return nil, err
-	}
-	userIDs := make([]string, len(users.Users))
-	for i, user := range users.Users {
-		userIDs[i] = user.ID
-	}
-	return userIDs, nil
+	return l.query.SearchClaimedUserIDsOfOrgDomain(ctx, orgDomain, "")
 }
 
 func setContext(ctx context.Context, resourceOwner string) context.Context {