Define what a marker team is

Currently we don't have a good definition of what a marker team is, or when it should be used. I think it would be helpful to define that more clearly.

Marker teams were introduced in https://github.com/rust-lang/team/pull/135 to accommodate the addition of icebreakers-llvm in https://github.com/rust-lang/team/pull/123, which was hooked up with triagebot to provide a way for people to ping a group of individuals who otherwise would not be members of the rust-org.

Over time, the use of marker-team has expanded organically to generally identify a group of people that need some kind of integration into our infrastructure, but otherwise are not members of the org. Some examples:

• Infrastructure accommodation:
  • docsrs-ops for permissions to manage docs.rs infrastructure, and crates-io-on-call and crates-io-admins for crates.io infrastructure.
  • cloud-compute to grant access to cloud computers
  • foundation-email-redirects
  • infra-admins
  • rustconf-emails
  • team-repo-admins
  • council-librarians -- Permissions to leadership-council repo.
  • hiring -- to create an email list
• Meta groups (to consolidate other groups for some purpose):
  • inside-rust-reviewers is a consolidation of other teams/members to provide an easier way to grant permissions.
  • all, leads, alumni, wg-leads, project-group-leads
• Ping groups:
  • android, windows, apple, arm, arm-maintainers, fuchsia, loongarch, risc-v, rust-for-linux, relnotes-interest-group, wasi, wasm, emscripten, icebreakers-llvm, icebreakers-cleanup-crew
• Things that probably should be teams:
  • emacs, vim, arewewebyet
• Satellite groups -- Groups with permissions (like GitHub), closely related, but not part of the org:
  • goal-owners
  • gsoc-contributors
  • mentors -- Not entirely sure what this does.
  • ospp, ospp-contributors

Another thought I had was to split marker-team into different classifications, like "meta-team" or "ping-group".

Review the marker-team introduction in PR #135 and the icebreakers-llvm setup in PR #123, then compare the infrastructure, meta, ping, and satellite examples listed here. Document a settled definition, guidance on when to use marker teams, and whether separate classifications are needed.