Suggestion comments

[balsoft]

Given I am logged in:

When I dismiss a suggestion
Then I MUST add a comment explaining the reason for dismissal

When I draft a suggestion
Then I CAN add a comment adding information to the issue

When I publish a suggestion
Then I SHOULD add a comment with additional information about the issue

Given I am logged in
When I view a suggestion
Then I see the comment with the suggestion

When I publish a suggestion
When the suggestion has an associated comment
Then the comment must be added prominently to the corresponding GitHub issue

[balsoft]

As a note: we can later add buttons/drop-down for pre-filling the comment with a set text for quicker dismissals.

[florentc]

I think this is a partial duplicate of #621.