feat: Skip adding PR comments for successful policy checks

[DazWorrall]

Community Note

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Overview of the Issue

We have policy checking enabled in our organisation, and the vast majority of PRs do not violate any of policies. That means for most of our changes, the Ran Policy Check comment is at best redundant and at worst a bit of a nuisance - it makes it harder for users to find and inspect the plan. The successful atlantis/policy_check CI status is sufficient to show that the policy checks have passed, so it would be great to have an option to disable the policy check comments unless there is a failure/violation.

[DazWorrall]

I would be willing to take look at this with some guidance - should there be a generic feature to classify messages as optional/informational and a config option to configure if they are posted, or a solution specific to the policy checking feature?

[DazWorrall]

Never mind, this was solved in #2405