[marlin] Bump version to 1.8.1 (10)

Summary: Add a script to make this easier and use it to bump the version.

Test Plan:

./scripts/bump-version.sh patch
pnpm bump-version minor

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D19540