creds: Add ImportCredential=

ImportCredential= takes a credential name and searches for a matching
credential in all the credential stores we know about it. It supports
globs which are expanded so that all matching credentials are loaded.

src/shared/bus-unit-util.c

@@ -1209,6 +1209,17 @@ static int bus_append_execute_property(sd_bus_message *m, const char *field, con
                 return 1;
         }
 
+        if (streq(field, "ImportCredential")) {
+                if (isempty(eq))
+                        r = sd_bus_message_append(m, "(sv)", field, "as", 0);
+                else
+                        r = sd_bus_message_append(m, "(sv)", field, "as", 1, eq);
+                if (r < 0)
+                        return bus_log_create_error(r);
+
+                return 1;
+        }
+
         if (streq(field, "LogExtraFields")) {
                 r = sd_bus_message_open_container(m, 'r', "sv");
                 if (r < 0)