Move certificates documentation into docs/ and update it for Vault secrets
- Move certificates documentation into docs/
- Add more details about how Certificates Updater functions
- Add steps for Vault secrets in GKMS section
- Remove manual procedure for Cloudflare certificates and mentions the Terraform managed certificates instead
- Cleanup, reformat, ...
Corrective action for https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/23709
Edited by Pierre Guinoiseau