Maintenance Mode Improvements (#6451)

* Custom migration step in tasks.py

- Add custom management command
- Wraps migration step in maintenance mode

* Rename custom management command to "runmigrations"

- Add command to isRunningMigrations

* Add new data checks

* Update database readiness checks

- Set maintenance mode while performing certain management commands

* Remove unused import

* Re-add syncdb command

* Log warning msg

* Catch another potential error vector

tasks.py

@@ -369,10 +369,9 @@ def migrate(c):
     print('Running InvenTree database migrations...')
     print('========================================')
 
-    manage(c, 'makemigrations')
-    manage(c, 'migrate --noinput')
+    # Run custom management command which wraps migrations in "maintenance mode"
+    manage(c, 'runmigrations', pty=True)
     manage(c, 'migrate --run-syncdb')
-    manage(c, 'check')
 
     print('========================================')
     print('InvenTree database migrations completed!')