[fix] container: setup minimal (#6268)

Start minimal, use defaults, and extend later on. The templates are no longer
checked for changes, which was confusing and annoying after a while.

See: https://github.com/searxng/searxng/issues/6261#issuecomment-4716008282

container/settings.template.yml

@@ -0,0 +1,8 @@
+# Read the documentation before extending the defaults:
+# https://docs.searxng.org/admin/settings/
+
+use_default_settings: true
+
+server:
+  secret_key: "ultrasecretkey"
+  image_proxy: true