new: added ``docker_get_uid_gid`` for charms.

bin/compose-core

@@ -1813,6 +1813,17 @@ docker_get_uid() {
 }
 export -f docker_get_uid
 
+docker_get_uid_gid() {
+    local service="$1" user="$2" group="$3" uid
+    uid_gid=$(cached_cmd_on_base_image "$service" "id -u \"$user\"; id -g \"$group\"") || {
+        debug "Failed to query for '$user' uid in ${DARKYELLOW}$service${NORMAL} base image."
+        return 1
+    }
+    info "uid from ${DARKYELLOW}$service${NORMAL} for user '$user' is '$uid_gid'"
+    echo "$uid_gid"
+}
+export -f docker_get_uid_gid
+
 
 logstdout() {
     local name="$1"