improve Dependabot Alert UI; allow markdown comments

[jtmoon79]

This is regarding the User Interface.

In my comment to close a Dependabot Alert, I created a markdown comment. That comment was saved as a plain-text comment with newlines removed. My closure explanation is difficult to read.
I would like to be able to create a normal markdown comment when closing a Dependabot Alert.

The closed Alert is here https://github.com/jtmoon79/super-speedy-syslog-searcher/security/dependabot/3
Screenshot at https://imgur.com/a/2Hvitg7

[erinhav]

Dependabot Alerts PM here 👋. I've forwarded this to our design team to get their thoughts!

[cb-bradbeebe]

+1 to this feature request; there's usually blocking issues/tickets/ongoing discussions and being able to reference them in the Dependabot UI via simple markdown comments (like the standard Github PR commenting UI) would be extremely useful; especially for enterprise GH customers.

cc: @erinhav

[erinhav]

Thanks! Would you be willing to chat more (async via email or sync via Zoom)? We're looking at improving ability to collaborate around alerts, so would love to hear your opinions. ✨