new: ``default-options`` in charm root is loaded as default options of service

bin/compose-core

@@ -1144,6 +1144,11 @@ get_compose_service_def () {
     [ -z "$service" ] && print_syntax_error "Missing service as first argument."
     docker_compose=$(get_compose_yml_content) || return 1
     result=$(_get_compose_service_def_cached "$service" "$docker_compose") || return 1
+    charm=$(echo "$result" |shyaml get-value charm 2>/dev/null) || return 1
+    if default_options=$(printf "%s" "$metadata" | shyaml -y -q get-value default-options); then
+        default_options=$(yaml_key_val_str "options" "$default_options") || return 1
+        result=$(merge_yaml_str "$default_options" "$result") || return 1
+    fi
     echo "$result" | tee "$cache_file" || return 1
 }
 export -f get_compose_service_def