Add operational guidance for pool tasks to SMI

Add operational guidance to support standard tasks performed as part of the pool preparations:

1. Taking and restoring database backups
2. Resetting user access (superseded by https://gitlab.developers.cam.ac.uk/uis/devops/digital-admissions/legacy-smi/-/issues/212)
3. Updating lookup group
4. Creating Google Drives
5. Creating PMOSs