feat: add custom install command support

[bahmutov]

Where you can overwrite the default Yarn or NPM install command

- name: Custom Yarn command
  uses: cypress-io/github-action@v2
  with:
    # https://classic.yarnpkg.com/en/docs/cli/install
    install-command: yarn --frozen-lockfile --silent

• closes Support for Yarn Berry #170

[github-actions]

🎉 This PR is included in version 2.7.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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