feat: all --octoherd-* flags are now optional

  BREAKING CHANGE: Repositories can no longer be passed as positional argument, use the `--octoherd-repos` (or `-R`) CLI flag instead.

  Before:

  ```
  npx @octoherd/script-add-octoherd-cli-to-script "@octokit/*"
  ```

  After

  ```
  npx @octoherd/script-add-octoherd-cli-to-script --octoherd-repos "@octokit/*"
  ```

  Or do not set `--octoherd-repos` at all, in which case the user will be prompted.

Author: gr2m