Claim snippet_id and organization_id for Cells

What does this MR do and why?

This MR registers two additional Cells claims so the Topology Service can enforce global uniqueness of these identifiers across cells:

• Snippets — Snippet now includes Cells::Claimable and claims its id (new SNIPPET_IDS bucket), with the owning organization as the claim subject.
• Organizations — Organization now claims its id (new ORGANIZATION_IDS bucket) in addition to the existing path claim.

References

• Feature issue:
  • Snippet ID gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#766 (closed)
  • Organization ID gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#768 (closed)
• Docs on how to claim an attribute: https://docs.gitlab.com/development/cells/claims/#how-to-claim-attributes

How to set up and validate locally

1. Enable the feature flags in the Rails console:

   Feature.enable(:cells_claims_snippets)
   Feature.enable(:cells_claims_organizations)

2. Create a snippet and an organization (UI or console).

3. Confirm that creating/updating/destroying these records triggers the corresponding claim create/destroy calls to the Topology Service (via the after_save/before_destroy hooks in Cells::Claimable), and that no claims are attempted when the flags are disabled.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist.