commit_subject: add a hook to check commit subjects

Fixes #7.
6 jobs for commit_subject-hook
Status Job ID Name Coverage
  External
failed kwrobot-branch-check

failed rust-git-hooks-megas-linux-debug

failed rust-git-hooks-megas-linux-debug

failed rust-git-hooks-megas-linux-debug

failed rust-git-hooks-megas-linux-debug

failed rust-git-hooks-megas-linux-debug

00:00:04