Consider adding web-features to the issue template

[zcorpan]

See discussion in #1034

This would involve changing at least ISSUE_TEMPLATE.md, gh-data.py, merge-data.py.

@captainbrosset said

Looking at activities.yml, it seems to me that you could almost get the caniuse, description, mdn, and url fields for free by linking your entries to web-features, which would simplify your file. Win-win 😄 ?

I suppose we could source those from web-features if not provided in the issue OP (or in activities.yml), or simplify if web-features coverage is good enough.