This makes it possible to enable pruning after the OptionsModel has been initialized and reset.
Partial backport of Core [[https://github.com/bitcoin/bitcoin/pull/16714 | PR16714]] - part 1 of 5
Commit [[https://github.com/bitcoin/bitcoin/pull/16714/commits/1957103786f97135f35ababc97efa1b481865eb0 | 1957103786f97135f35ababc97efa1b481865eb0]]