v8.4.0 — instance component: promote_runner_tag + vm_size inputs

Catches the instance component up to base-build-scratch's estate-runner
inputs (promote-lane split from v8.3.0 + VM sizing from v8.2.0). Fixes the
MR-pipeline wedge where pinning the whole component to the ref_protected
crucible runner left detect-changes stuck_pending_no_matching_runners on
unprotected MR refs. See CHANGELOG.md.