Update shared credentials, secrets and external account page
This page is out of date and should be updated
https://guidebook.devops.uis.cam.ac.uk/en/latest/workflow/credentials-and-secrets/
- confirm with Service Managers that recovery e-mails addresses are set
- Add section about using 1Password
- Add section about using Google Secrets Manager
- Should this page link to https://guidebook.devops.uis.cam.ac.uk/en/latest/deployment/secrets/