Auto-create tracking issues for accepted MCPs

[fmease]

Implements accepted MCP #892.

Open to wording suggestions by anyone.

[apiraino]

@fmease Why create the template here instead of a GitHub issue template? Is it because how the handler major_change work? Asking without having looked at the code of that handler.

[fmease]

@apiraino GitHub issue templates are for humans, this issue template on the other hand is for triagebot which will use it to automatically create an issue in r-l/r after filling out the form substituting all placeholders.

[Urgau]

Looks good to me.

I will let it open a few days for anyone to comment.

[apiraino]

The content of the template looks good (as far as I can see).

I pasted it into a GH new issue to see how it looks:

screenshot

I wish we could perhaps collaps behind a <details> part of that note (I am somehow fixated with reducing visual clutter as much as possible) but I can't immediately identify parts that are less important to know for a casual reader. So I guess it's fine like this?

See the MCP template:
https://togithub.com/rust-lang/compiler-team/issues/934#issuecomment-3441667549