Issue template format should be more forgiving

[jolheiser]

The recently merged #11450 contains a potential flaw.

The problem

Using the example I added to the docs

-----
name: "Template Name"
about: "This template is for testing!"
title: "[TEST] "
labels:
  - bug
  - "help needed"
-----
This is the template!

will not actually work.

This is because the ExtractMetadata func actually tries to parse everything within the separators, including the separators themselves. As a matter of fact if you look closely at the above block, syntax highlighting reveals the issue with the - separators.

While YAML does allow a similar format for "blocks", those must be three hyphens, which means currently issue templates expect a specific number of hyphens to work.

The solution

The ExtractMetadata func should only parse between the lines, e.g.

name: "Template Name"
about: "This template is for testing!"
title: "[TEST] "
labels:
  - bug
  - "help needed"

This would allow users to use any amount of hyphens (as long as it's two or more so that lists aren't confused as separators)