feat: add plan_requirements capability

[lyoung-confluent]

what

• Add a new key plan_requirements mirroring the existing apply_requirements and import_requirements keys, but for atlantis plan.

why

• This can be used to apply restrictions before a plan is executed, such as mandating peer review.

tests

• I have added tests for all of the new code, mirroring the existing tests for apply/import.

references

• closes plan_requirements (similar to apply_requirements) #2073

[krrrr38]

@lyoung-confluent FYI plan_command_runner may need this impl too https://github.com/krrrr38/atlantis/blob/c6f59309ec5f635f942e519f698397e328cbdde1/server/events/import_command_runner.go#L31-L43

(ctx.PullRequestStatus is mutable value and it requires to be set by command runner now.)

[nitrocode]

Why is this needed?

[camillsir]

This is addressing @krrrr38's comment. For this change we are checking approved and mergeability states during plan and those checks require ctx.PullRequestStatus to be populated. What I saw when testing this without these lines is that the plan was correctly blocked by the approval check, but it would never succeed as the approval status was not updated during a plan run.

[krrrr38]

This field is useful and we forget to fill-in. So ctx.PullRequestStatus might be better to fill-in at the instance creation timing

atlantis/server/events/command_runner.go

Lines 150 to 158 in cb0aadf

	ctx := &command.Context{
	User: user,
	Log: log,
	Scope: scope,
	Pull: pull,
	HeadRepo: headRepo,
	PullStatus: status,
	Trigger: command.AutoTrigger,
	}

But it requires apply_command_runer/import_command_runner change too, so I think it doesn't need it in this PR.

[nitrocode]

@krrrr38 did your suggestion get implemented? can this comment be resolved? I assume it can since you posted "LGTM" 😄

[krrrr38]

The above impl is optional in this PR and not need to do it in this PR, so resolved 👍

[krrrr38]

LGTM

[nitrocode]

Thank you @lyoung-confluent ! Your feature will be available in the dev tag after the build finishes and then officially upon the next release. Please test the feature for any bugs prior to the next release. 🙏

Feel free to propose more changes! Thank you again