core: add CoredumpReceive= setting

This setting indicates that the given unit wants to receive coredumps
for processes that crash within the cgroup of this unit. This setting
requires that Delegate= is also true, and therefore is only available
where Delegate= is available.

This will be used by systemd-coredump to support forwarding coredumps to
containers.

src/shared/bus-unit-util.c

@@ -565,7 +565,8 @@ static int bus_append_cgroup_property(sd_bus_message *m, const char *field, cons
                               "IOAccounting",
                               "BlockIOAccounting",
                               "TasksAccounting",
-                              "IPAccounting"))
+                              "IPAccounting",
+                              "CoredumpReceive"))
                 return bus_append_parse_boolean(m, field, eq);
 
         if (STR_IN_SET(field, "CPUWeight",