Remove the memonly bool and follow the Add and Load pattern we use
everywhere else.
This is a backport of [[https://github.com/bitcoin/bitcoin/pull/19046 | core#19046]] [2/3]
https://github.com/bitcoin/bitcoin/pull/19046/commits/d9cd095b5965fc20c09f401370e7ba99446663e3
Depends on D9630