feat: introduce setup hook option - #1326

Closes #1218

Context

Sometimes special "pre-run" actions are required for hook jobs to be run correctly. Moving it to a first job may be a good solution, but such approach is quite limited.

So, setup option is here to fill the gap.

# lefthook.yml

pre-commit:
  setup:
    - run: mise install
  jobs:
    - run: bundle exec ...
    - run: node scripts/some-script.js
    - run: cargo ...

setup option has good potential for more things that include preparing the environment for pre-commit jobs. setup instructions must be idempotent to make conditions repeatable and stable.

Changes

• Add setup option to config
• When merging setup always prepend new instructions (the opposite to extend logic)
• Execute setup instructions before running all jobs
  • Support templates replacement
  • Log separately
  • Add a separate output log control
• Add tests
• Add docs