Factory Assistant update channel

Endpoints served from this site:

• stable.json — the stable update channel the appliance polls
• beta.json — the beta update channel endpoint
• dev.json — the dev update channel endpoint
• apparmor_stable.txt — Supervisor AppArmor profile
• apparmor_beta.txt — Supervisor AppArmor profile for beta
• apparmor_dev.txt — Supervisor AppArmor profile for dev
• schema/channel.schema.json — channel document schema