feat(github-action): Implement cfn-guard as a Github Action in TS

[dannyvassallo]

Issue #, if available: N/A

Description of changes:

Utilizes the cfn-guard TS lib inside of a github action.

File changes primarily exist under action/src, action/__tests/, .github/workflows, and action.yml on the root.

If you want to read the changes like a compiler, start at action/src/main.ts

THIS DOES NOT INCLUDE FURTHER ATTRIBUTION AND DOES NOT INCLUDE README UPDATES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[joshfried-aws]

Asside from some nits, this looks good to me.

I think we should add some lints. Personally I think we should enforce ; at the end of statements. I personally find it much easier to read with them.

[dannyvassallo]

Asside from some nits, this looks good to me.

I think we should add some lints. Personally I think we should enforce ; at the end of statements. I personally find it much easier to read with them.

Added semi rule with autoformatting.

[benbridts]

Hey folks, I think this is awesome (looking very much forward to using it)!

One thing that would be interesting to consider (that's kinda independent of this PR), is if this should (also?) exist under https://github.com/aws-actions.
The main reason for that would be organisations allow-listing actions that can be used in their org. I think in practice it won't be a big hurdle to get both aws-actions and aws-cloudformation in an allow list, but for places where aws-actions is already allowed it's one step less.

[dannyvassallo]

Hey folks, I think this is awesome (looking very much forward to using it)!

One thing that would be interesting to consider (that's kinda independent of this PR), is if this should (also?) exist under https://github.com/aws-actions. The main reason for that would be organisations allow-listing actions that can be used in their org. I think in practice it won't be a big hurdle to get both aws-actions and aws-cloudformation in an allow list, but for places where aws-actions is already allowed it's one step less.

@benbridts Hey! Great suggestion. During design we'd considered having the action live in it's own repo outside of the guard monorepo but ultimately decided on nesting it here. It's something to talk about though so while we have it here at least for now to do some testing, I'm bringing this back to the team to discuss. Thank you!