Use a local SQLite3 backend instead of PostgreSQL Docker container.

* The provided SQLite3 database contains the required schemas, but no data and can be reset to if required.
* Remove all references to PostgreSQL in documentation and configuration.
* Replace native sqlite3 command with a console app to remove dependency on SQLite3 installation.

service/appsettings.json

@@ -7,5 +7,5 @@
     }
   },
   "AllowedHosts": "*",
-  "PostgresConnection": "Server=localhost;Database=mydatabase;User Id=user;Password=password;"
-}
+  "SqliteConnection": "Data Source=service.db"
+}