[Workflows/Docs] Canonical labels + org seeding workflow

[ashleyshaw]

Title: [Workflows/Docs] Canonical labels + org seeding workflow
Labels: area:workflows, v0.2.0, labeling
Acceptance Criteria:

automation/labels.yml includes name/colour/description + deprecations.

labeling.yml seeds/syncs idempotently; safe to re-run.
Owner: Workflows