chore: add `good first issue` label comment (#61215)
### What?
Add a comment to issues labeled with `good first issue`. Rendered
comment
[here](https://github.com/vercel/next.js/blob/b868cf95f29a305bca1afabdb8db76e64a1cce30/.github/good-first-issue.md).
### Why?
We have historically marked issues with this label, but rarely did it
make someone contribute. A few times I have seen people asking for
permission first instead of contributing. This comment will clarify the
fact that they can just do so.
### How?
Using `nissuer`'s
[comment-label](https://github.com/balazsorban44/nissuer#label-management).
Closes NEXT-2256
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Co-authored-by: Steven <steven@ceriously.com>
