Add common saved replies for issue triaging

[Noratrieb]

I've recently started to write saved replies for triaging. It would be nice to share them here so people can use the same replies. We can also iterate on them together to ensure high quality.

For example, what I've created:

Closing this issue as unactionable. If you can provide a reproduction, we can re-open the issue, but without one, there is nothing we can do.

Thank you for the report! It would be useful to bisect the regression using cargo-bisect-rustc to make it easier to figure out what happened and ping the relevant people

Thank you for the PR! This PR contains a public library API change, which should follow the proper process: https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html

The last one isn't about issues but is still useful.

[apiraino]

great idea, if you intend to add them to the forge documentation (I think I would look for them there). And people can copy and save them as "saved replies" for comment templates.

[apiraino]

IIRC template comments for pull requests are handled by the triagebot (I think here) based on the codepaths changed by the patch. I'm thinking if these kind of automessages should go there