Add a structured bug report template

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What this PR does / why we need it:

I see there are 1100 issues on this repo, and that @J-Fields does much of the triaging as well as the development. Would a more structured issue log template increase the quality of issues? I see a mixed bag out there — e.g. #7274, #7270, #7262, #7223 would probably be more helpful to both the reporter and the project if they added more detail.

A few ideas contained here:

• Use the new structured yaml format for issues
• Ask people to fill out a "machine-readable" testcase where possible.
  • This is probably a minority of issues but some recent ones where this would help are A way to jump to matching quotes (similar to % for brackets)? #7214, Unexpected behavior with vito #7245, Surrounding selection with quotes #7159, Double paired elements(e.g. brackets/parentheses) break words in placeholders in snippets #7213, <C-t> does not move the cursor after the first indent #7204, <Home> and <End> don't work the same in normal and insert mode #7168, CamelCaseMotion is not ignoring underline #7095) .
  • As well as removing ambiguity, it's also a testcase that development can start from — a way to shift burden from maintainers & contributors to the original reporter.
  • Another option would be to split this into a different type of bug report
• Ask people to confirm the bug isn't a duplicate

We don't have to take all of these at once if some of them aren't good ideas.

Rendered version

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@J-Fields let me know if something like this would be of interest — no problem if not!