CI/CD improved.

Migrated to GitHub registry.
Migrated to JDK21, Virtual Threads were turned on.
Migrated to Postgres 16.1.
Default caches turned on.

Data Generator migration problems were fixed.

.github/workflows/gradle.yml

@@ -11,7 +11,7 @@ on:
   schedule:
     - cron: '0 0 1 * *' # every 1st day of month
 #  push:
-#    branches: [ "master" ]
+#    branches: [ "main" ]
 
 permissions:
   contents: read