[backport] wallet: Replace `%w` by wallet name in `-walletnotify` script
Summary
This is a backport of bitcoin core PR 13339. This closes #479 (closed). It adds %w
support in addition to %s
support for the -walletnotify=
command-line.
Merge instructions: Do not squash, so as to preserve commit history and attribution.
Test Plan
ninja all check-all