fix: [compose-core] display errors when running action and constraints are not verified

Before it would quit without any notice. A message is also added for a
common fix when constraints fails unexpectedly.

bin/compose-core

@@ -2611,7 +2611,8 @@ get_all_relations () {
                 providers_def=()
                 array_read-0 providers providers_def < <(_get_charm_providing "$relation_name" "${service_list[@]}")
                 if [ "${#providers[@]}" == 0 ]; then
-                    die "Summoning a ${DARKBLUE}$relation_name${NORMAL} provider failed: none were found in charm store."
+                    err "Summoning a ${DARKBLUE}$relation_name${NORMAL} provider failed: none were found in charm store."
+                    return 1
                 fi
 
                 if [ "${#providers[@]}" -gt 1 ]; then
@@ -4322,7 +4323,10 @@ if [ -z "$is_docker_compose_action" -a "$action" ]; then
             esac
         } < <(has_service_action "$action_service" "$action")
         services_args=("$action_service")
-        get_all_relations "${services_args[@]}" >/dev/null 2>&1 || exit 1
+        get_all_relations "${services_args[@]}" >/dev/null || {
+            echo "  Hint: if this is unexpected, you can try to delete caches, and re-run the command." >&2
+            exit 1
+        }
 
         ## Divert logging to stdout to stderr
         log () { cat >&2; }