Netmaker add-on: pull prebuilt image from Gitea registry

Home Assistant add-on that joins the instance to a Netmaker network via
netclient. Distributed as a repository add-on using a prebuilt arm64 image
(gitea.savant.io/homeassistant/netmaker) to avoid local buildx.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

netmaker/rootfs/command/with-contenv-merge

@@ -0,0 +1,14 @@
+#!/command/execlineb -S0
+
+ifelse
+{
+  importas -D 0 S6_KEEP_ENV S6_KEEP_ENV
+  eltest 0${S6_KEEP_ENV} -eq 0
+}
+{
+  s6-envdir -Lf -- /run/s6/container_environment
+  exec
+  $@
+}
+
+$@