Toggle show/hide all issue comment attributions

#2340363: Add issue comment attribution suggested putting the toggle next to the "Attribute this contribution" section of the comment form. This is good for grouping related functionality, but has potential drawbacks:

• The actual toggling has a good chance of being off-screen. We need to make sure people have a good chance of learning what this does.
• There isn't a comment form for anonymous users, so it would stay at the default.

A double click toggle, consistent with date formatting, is possible. However, it does have drawbacks too #2280497: Comments no longer show the date they were posted, notably accessibility. Consistency for all these little toggles would be good.

Another suggestion I remember from #2340363: Add issue comment attribution is putting it in the sidebar. I can't think of any big advantages or drawbacks.

On toggling in general - more toggles is more complexity for the issue page, which is already full of it. We should be careful when adding settings.