This makes it possible to enable pruning after the OptionsModel has been initialized and reset.
Backport of Core PR16714 - part 1 of 4
Commits:
[[https://github.com/bitcoin/bitcoin/pull/16714/commits/1bccf6a52d7fc08d8f605cfb2edc3277ec299c72 | 1bccf6a52d7fc08d8f605cfb2edc3277ec299c72]]
[[https://github.com/bitcoin/bitcoin/pull/16714/commits/1957103786f97135f35ababc97efa1b481865eb0 | 1957103786f97135f35ababc97efa1b481865eb0]]