feat: Move silence tracking, remove old Cx mapping reference.

What

• Move silence tracking out to its own project
• Remove old Cx mapping reference.

Why

Silence tracking is now easier to update in the editable table here. Most silences are across more than one tenant, so this is also now consolidated into a single step to review instead of splitting it across multiple people.

Separate repo has the benefit of:

• Previewable markdown isntead of inlining inside YAML.
• Can be changed quickly without an MR. Silences can be quite short term and dynamic.
• Moves the silences to a private project. triage-ops is open to the public.
• Most current silences have been pushed down a few months, no need to clutter the weekly template with them.