Update -banscore and -bantime help text

Summary:
See https://github.com/bitcoin/bitcoin/pull/19219/commits/b691f2df5f7d443c0c9ee056ab94aa0fc19566d5#diff-c865a8939105e6350a50af02766291b7
This commit was backported before being merged upstream, so this patch adds some parts
that are missing now that it has been merged.

Test Plan:

ninja check
bitcoind --help    # verify new help text

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D6864