wallettool: Add a salvage command
Summary:
Partial backport (1/11) of core PR18918:
https://github.com/bitcoin/bitcoin/pull/18918/commits/c87770915b88d195d264b58111c64142b1965cfa
Test Plan:
ninja all check-all bitcoin-wallet --help | grep -C1 salvage
Reviewers: #bitcoin_abc, majcosta
Reviewed By: #bitcoin_abc, majcosta
Differential Revision: https://reviews.bitcoinabc.org/D8588