Refactor db code. Add migration support

sqlc.yml

@@ -1,9 +1,13 @@
 version: "2"
 sql:
   - engine: "sqlite"
-    queries: "db/query.sql"
-    schema: "db/schema.sql"
+    queries: "internal/repository/sql/"
+    schema: "internal/repository/migrations/"
     gen:
       go:
         package: "repository"
         out: "internal/repository"
+        emit_db_tags: true
+        emit_json_tags: true
+        json_tags_case_style: "camel"
+        emit_pointers_for_null_types: true