Feature Request: allow steps to add cache paths

This would allow steps to add paths to cache. This should be usefull to write e.g. setups for package managers as steps:

Example:

# pnpm setup step
spec:
  inputs:
    version:
      type: string
---
exec:
  command:
    - bash
    - -c
    - whatever-setup.sh

this whatever-setup.sh could do

    - corepack enable
    - corepack prepare pnpm@latest --activate
    - pnpm config set store-dir .pnpm-store

in this case it should be possible to add the store as cache.

cache:
    policy: pull-push
    key:
      files:
        - pnpm-lock.yaml
      prefix: pnpm-store
    paths:
      - .pnpm-store