feat!: migrate edge & proxy to new builder

[Nerivec]

• Use HA-provided builder workflow with small modifications to better fit use cases
• Rewrite to use s6-overlay & co, and improve configuration handling
• ⚠️ BREAKING: Use addon_config mapping. See migration
  • Config folder is now included in Home Assistant add-on backups
  • Each add-on now has its own config folder (if wanting to switch between regular and edge add-ons, you must copy over the data)
  • The toggle to delete the add-on data when uninstalling the add-on will now remove your Zigbee2MQTT configuration (yaml, db, logs, etc.)
• All configuration.yaml settings are now handled either through the onboarding (can be forced in add-on configuration tab), the frontend once Zigbee2MQTT has started, or directly in the file itself (using add-on) while Zigbee2MQTT is stopped
• The Zigbee2MQTT watchdog is now enabled by default, with default settings
• [ADVANCED] For easier debugging, can now override app code through app_overrides folder in add-on config folder
  • On add-on start, if the app_overrides folder exists, its content is copied over the Zigbee2MQTT app folder (using exact folder structure)
  • Deleting the app_overrides folder will remove any override on next add-on start

See Nerivec/ha-zigbee2mqtt#2 for previous auto-migration testing details.

See https://github.com/Nerivec/zigbee2mqtt-windfront/blob/5fd113b61b0ce34ad0dce355c38cfd43c049dc51/.github/workflows/ci.yml#L138-L147 for example use of the manual-builder workflow (example run)

See https://github.com/Nerivec/zigbee2mqtt-windfront/blob/5fd113b61b0ce34ad0dce355c38cfd43c049dc51/.github/workflows/ci.yml#L149-L158 for example use of the bump-version workflow (example result PR)

See https://github.com/Nerivec/ha-zigbee2mqtt-windfront/actions/runs/19746873199 for example run of builder workflow (from merging PR created by above workflow - auto detect changes).

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This does not migrate the "regular" add-on, will be done separately (dedicated folder, common folder & workflows remain the same).