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

@@ -0,0 +1 @@
+[]

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

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+{}