feat: add hide-unchanged-plan-comments option

[tufitko]

what

Add hide-unchanged-plan-comments options to removing useless no-changes plans from comments.

why

In our repository we have a lot of terragrunt projects. Sometimes we have big pull requests (for example with ~600 projects, usually about 5-6 plans has changes) and It's hard to review.

tests

some tests are added

1 / 6 project with changes

two projects, no changes, nothing to show

without flag output is

...

[nitrocode]

Thank you @tufitko ! Please feel free to send more PRs :)

[nitrocode]

@tufitko been playing around with the feature today

What if we also skipped atlantis apply on "no changes" plans. Basically to do this, we see if the plan is a no-change and just omit the plan file for that directory.

We'd have to be careful since if there is a change in terraform outputs, it would still say "no changes" but there would technically be a change.

[tufitko]

@nitrocode hmm, I'm not sure how atlantis works with terraform apply... Does it show the plan in applying stage? or we should use the plan from the planning stage?
In terragrunt's case, we should generate a new plan on apply and don't use plan from planning stage. so we can just copy logic from planning 🤔
In my team big apply's output isn't a problem, I didn't even think about it

[tufitko]

@nitrocode oh, also, in the case of plans, we still can see the plan's output in Atlantis UI, but after PR was merged we aren't able to see outputs at all, except comments in PR