Move DB handling into specialised classes

This keeps CuraContainerRegistry a lot cleaner, especially when more container types are
added

Cura-6096

cura/Settings/DatabaseHandlers/VariantDatabaseHandler.py

@@ -0,0 +1,29 @@
+from UM.Settings.DatabaseContainerMetadataController import DatabaseMetadataContainerController
+from UM.Settings.InstanceContainer import InstanceContainer
+
+
+class VariantDatabaseHandler(DatabaseMetadataContainerController):
+    def __init__(self) -> None:
+        super().__init__(
+            insert_query= "INSERT INTO variants (id, name, hardware_type, definition, version, setting_version) VALUES (?, ?, ?, ?, ?, ?)",
+            update_query= "",
+            select_query= "SELECT * FROM variants where id = ?",
+            table_query="""CREATE TABLE variants
+                (
+                    id text,
+                    name text,
+                    hardware_type text,
+                    definition text,
+                    version text,
+                    setting_version text
+                );
+                CREATE UNIQUE INDEX idx_variants_id on variants (id);"""
+        )
+
+    def _convertRawDataToMetadata(self, data):
+        return {"id": data[0], "name": data[1], "hardware_type": data[2], "definition": data[3], "container_type": InstanceContainer, "version": data[4], "setting_version": data[5], "type": "variant"}
+
+
+    def _convertMetadataToInsertBatch(self, metadata):
+        return metadata["id"], metadata["name"], metadata["hardware_type"], metadata["definition"], metadata["version"], \
+               metadata["setting_version"]