Remove memonly bool and follow typical Add and Load pattern used
everywhere else.
This is a backport of [[https://github.com/bitcoin/bitcoin/pull/19046 | core#19046]] [3/3]
https://github.com/bitcoin/bitcoin/pull/19046/commits/3a9aba21a49a6d80bd187940d5e26893937b6832
Depends on D9631