Support `atlantis test` subcommand

[nitrocode]

Community Note

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• [ ] I'd be willing to implement this feature (contributing guide)

Describe the user story

Support terraform test

Describe the solution you'd like

See above

Describe the drawbacks of your solution

None

Describe alternatives you've considered

N/A

references

• https://github.com/runatlantis/atlantis/issues/2776