fix(repo): correct mapping for domains (#10653)

This pull request fixes an issue where the repository would fail to scan
organization or instance structs if the `domains` column was `NULL`.

## Which problems are solved

If the `domains` column of `orgs` or `instances` was `NULL`, the
repository failed scanning into the structs. This happened because the
scanning mechanism did not correctly handle `NULL` JSONB columns.

## How the problems are solved

A new generic type `JSONArray[T]` is introduced, which implements the
`sql.Scanner` interface. This type can correctly scan JSON arrays from
the database, including handling `NULL` values gracefully.

The repositories for instances and organizations have been updated to
use this new type for the domains field. The SQL queries have also been
improved to use `FILTER` with `jsonb_agg` for better readability and
performance when aggregating domains.

## Additional changes
* An unnecessary cleanup step in the organization domain tests for
already removed domains has been removed.
* The `pgxscan` library has been replaced with `sqlscan` for scanning
`database/sql`.Rows.
* Minor cleanups in integration tests.

backend/v3/storage/database/events_testing/instance_test.go

@@ -45,13 +45,13 @@ func TestServer_TestInstanceReduces(t *testing.T) {
 		})
 
 		retryDuration, tick := integration.WaitForAndTickWithMaxDuration(CTX, time.Minute)
-		assert.EventuallyWithT(t, func(ttt *assert.CollectT) {
+		assert.EventuallyWithT(t, func(t *assert.CollectT) {
 			instance, err := instanceRepo.Get(CTX,
 				database.WithCondition(instanceRepo.IDCondition(instance.GetInstanceId())),
 			)
-			require.NoError(ttt, err)
+			require.NoError(t, err)
 			// event instance.added
-			assert.Equal(ttt, instanceName, instance.Name)
+			assert.Equal(t, instanceName, instance.Name)
 			// event instance.default.org.set
 			assert.NotNil(t, instance.DefaultOrgID)
 			// event instance.iam.project.set