First step towards auto-triaging PRs by adding the "awaiting-review" and "team-X" labels.

(Starting with just team-ExternalDeps to see if things go smoothly, before adding the others)

cc @Wyverald

Closes #17833.

PiperOrigin-RevId: 518347085
Change-Id: Ie601f71fb8ea359aadb4174a3fa592fd5ffe219f