cgroup: Create UNIT_DEFINE_ANCESTOR_MEMORY_LOOKUP
This is in preparation for creating unit_get_ancestor_memory_min.
(cherry picked from commit 6264b85e92aeddb74b8d8808a08c9eae8390a6a5)
Related: #1763435
patch_name: 0407-cgroup-Create-UNIT_DEFINE_ANCESTOR_MEMORY_LOOKUP.patch
present_in_specfile: true
location_in_specfile: 407
squash_commits: true