meta: add some sort of auto-triage

[gsnedders]

There's various bits of auto-triaging we could do when an issue is filed; from the spec URL we can infer the venue of the work, and in many cases we can infer topic from that too.

[hober]

We now have the backlog project Standards Positions Review Backlog for this, but automatically adding a new issue to the project requires additional GitHub Actions fu. I'm hoping to figure this out in the next week or so.

[hober]

Note to self: close #66 when you have this in place.

[gsnedders]

fwiw, see:

https://github.com/orgs/community/discussions/6838
https://github.com/zentered/issue-forms-body-parser
https://github.com/stefanbuck/github-issue-parser
https://github.com/peter-murray/issue-forms-body-parser

and also https://github.com/w3c/browser-specs is probably useful as a data source