Update Cloudflare documentation to reflect new rule management process
As part of ongoing Cloudflare improvements work, the Foundations team has moved all Cloudflare configuration to be managed via Terraform. This MR is intended as a proposal of the new process for managing Cloudflare settings (especially rule creation).
See gitlab-com/gl-infra/production-engineering#24689 (closed)
OKR: https://gitlab.com/gitlab-com/gitlab-OKRs/-/work_items/5390
Edited by Sarah Walker