[Bookworm] Correct Flask DB migration process

Move the old manage script to _legacy, and add a new _flask version with
modern Flask tooling. Decide which one to call via pvc-api-db-migrate
using /etc/debian_version call.

api-daemon/pvcapid-manage_legacy.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+
+# pvcapid-manage_legacy.py - PVC Database management tasks (Legacy)
+# Part of the Parallel Virtual Cluster (PVC) system
+#
+#    Copyright (C) 2018-2022 Joshua M. Boniface <joshua@boniface.me>
+#
+#    This program is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License as published by
+#    the Free Software Foundation, version 3.
+#
+#    This program is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#
+###############################################################################
+
+from flask_migrate import Migrate, MigrateCommand, Manager
+
+from pvcapid.flaskapi import app, db
+from pvcapid.models import *  # noqa F401,F403
+
+migrate = Migrate(app, db)
+manager = Manager(app)
+
+manager.add_command("db", MigrateCommand)
+
+if __name__ == "__main__":
+    manager.run()