Invoke shipjs prepare from GitHub

shipjs trigger can be automated thanks to CI. To achieve frictionless release flow within the GitHub interface, shipjs prepare must also be able to be invoked without manually typing the CLI command from someone’s PC.

Possible solution

1. Invoke shipjs prepare when someone responsible for releasing process and granted for running it (basically, admin) comments @shipjs prepare in an issue or PR.
2. Offer simple Web UI (like Dependabot) to provide the Prepare Release button.
3. (any thoughts?)

[uetchy]

@eunjae-lee @KnisterPeter I’ve been thinking about that. Maybe we can do that on GitHub Actions, without concerning maintaining servers:

on:
  issue_comment:
    types: created
jobs:
  manual_release:
    if: |
      github.event_name == 'issue_comment' &&
      (github.event.comment.author_association == 'member' || github.event.comment.author_association == 'owner') &&
      startsWith(github.event.comment.body, '@shipjs prepare')
    runs-on: ubuntu-latest
    steps:
      - run: shipjs prepare

In that case, however, we have to resolve #316 first to ensure shipjs is compatible with GitHub Actions.

[KnisterPeter]

@eunjae-lee Github Actions could react on comments in issues or PRs.