Improvements to GitHub App Plan Comments

[datfinesoul]

Is your feature request related to a problem? Please describe.

Describe the solution you'd like

Since these plans show up every time a change is made, It would be nice if the entire comment was in a collapsible block, or if the comment block is re-used instead of having multiple of them pile up.

1. In it's current form, I feel like this section doesn't really provide a lot of useful info.
   • "Distinct actions" doesn't mean anything to me. If this is meant to be add/update/delete, then having some abbreviated counts here might be good.
   • "Templates with changes" is too high level to be meaningful. Breakdown by resource type here might nice, in favor of removing clicks from 4)
   • "Accounts" is moderately useful, because it gives some meaningful scope.
     In its current form, I'd almost rather have this section be collapsed to save room.
2. If there are no exceptions, it would be great if this section could just be omitted. This is just extra text when there are no errors.
3. This section is too click intensive. This is the information I would like to see the most. I believe the number of collapsible sections here is too high for somebody to effectively use this comment as a way to review the plan.
4. The run link for me pointed to https://github.com/undefined-io/iambic-templates/pull/None, which was a 404. It's also just not clear what "run" in this context actually means. If this section could instead include information about running apply using iambic apply that would be a bit more useful. Or at least a link to the docs about what to do next.

Describe alternatives you've considered
The main thing about these types of PR comment plans should be to provide as much easily reviewable information as possible in the smallest amount of space, with the least amount of clicks IMO. Anything that is no helpful to a reviewer doesn't need to be shown. And if there are links, it should be clear what they will do when clicked.

Additional context

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