Configure Home Assistant Podman container

The default Home Assistant configuration does not allow running a
reverse proxy in front of the application.  To enable this, the
`use_x_forwarded_for` and `trusted_proxies` options have to be set.

Since we want `/var/lib/homeassistant` to be a Btrfs subvolume, we can't
simply include the necessary files in the correct location in the rootfs
image.  Instead, we must define "copy tree" (`C`) actions for
`systemd-tmpfiles` to copy them from `/usr/share/factory`.
Unfortunately, `systemd-tmpfiles` considers `v` and `C` actions
conflicting, and thus will not copy the directory contents recursively.
Each file has to be listed explicitly.

yellow/overlay/etc/containers/systemd/home-assistant.container

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+[Unit]
+After=network-online.target
+Wants=network-online.target
+
+[Container]
+Image=ghcr.io/home-assistant/yellow-homeassistant:stable
+Network=host
+Volume=/var/lib/homeassistant:/config:Z
+User=300
+Group=300
+ReadOnly=true
+VolatileTmp=yes
+
+[Service]
+TimeoutStartSec=5min
+UMask=0077
+
+[Install]
+WantedBy=multi-user.target

yellow/overlay/etc/sysusers.d/homeassistant.conf

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+u homeassistant 300 "Home Assistant" /var/lib/homeassistant /bin/sh
+g homeassistant 300

yellow/overlay/etc/tmpfiles.d/homeassistant.conf

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+v /var/lib/homeassistant 0700 homeassistant homeassistant - -
+C /var/lib/homeassistant/automations.yaml - - - -
+C /var/lib/homeassistant/configuration.yaml - - - -
+C /var/lib/homeassistant/groups.yaml - - - -
+C /var/lib/homeassistant/http.yaml - - - -
+C /var/lib/homeassistant/scenes.yaml - - - -
+C /var/lib/homeassistant/scripts.yaml - - - -
+C /var/lib/homeassistant/secrets.yaml - - - -

yellow/overlay/usr/share/factory/var/lib/homeassistant/automations.yaml

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+[]

yellow/overlay/usr/share/factory/var/lib/homeassistant/configuration.yaml

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+
+# Configure a default setup of Home Assistant (frontend, api, etc)
+default_config:
+
+http: !include http.yaml
+
+# Text to speech
+tts:
+  - platform: google_translate
+
+group: !include groups.yaml
+automation: !include automations.yaml
+script: !include scripts.yaml
+scene: !include scenes.yaml

yellow/overlay/usr/share/factory/var/lib/homeassistant/http.yaml

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+server_host: '::1'
+trusted_proxies:
+- '::1'
+use_x_forwarded_for: true

yellow/overlay/usr/share/factory/var/lib/homeassistant/secrets.yaml

@@ -0,0 +1 @@
+{}