Improvements and fixes

Note: see also Github Issues

P2 Memory consumption: Even an empty App Engine app (not Iris, just a Hello World with 3 lines of code in total) crashes on out-of-memory for the smalled App Engine instance. Google has confirmed this. See if there is a workaround. This will save money.
P3 Label immediately after an event in certain cases, as opposed to using a daily cron as is now done.
- Cloud SQL Instances
  - See above re Cloud Tasks
- Boot disks that are created with the instance
  - This is done by pulling a list of disks from the information about the instance. See GCP Auto Tag,
- The attachment status of disks
  - When attachment status changes, a label needs to change from false to true or vice versa.
  - Current code does it on cron schedule.
  - We could do it on-event by capturing the log for the attachment event, just as we already capture logs for creation events.
P3 Address the error "Labels fingerprint either invalid or resource labels have changed", printed in _batch_callback, which occurs intermittently, especially with disks. Solutions:
- Retry
- Ignore and let the cron do it
- Implement Cloud Task with a delay. (Not clear if that will help.)
P3 Rethink the need for title case in class names. This is clumsy for Cloudsql.
P4 Implement new labels, for example using ideas from the GCP Auto Tag project But don't add too many: There are a lot of fields on resources.
- Add a label with the email of the creator of the resource