[Feature request] Add action typings

[krzema12]

Hi @actions-rs!

Maintainer of https://github.com/krzema12/github-actions-kotlin-dsl here. Your actions have first-class support in the library.

Recently we've come up with a way to reduce operational load when keeping library's action wrappers in sync with action's inputs. The solution includes onboarding https://github.com/krzema12/github-actions-typing. It's as easy as adding an extra YAML file to your repository root, and adding a simple GitHub workflow that validates this new file. Thanks to this, the code generator in the Kotlin DSL can fetch typing info provided by you instead of us, which has a number of benefits. It has no negative effects on current action consumers, they continue to use the action via regular GitHub API, as if the file wasn't there. The typings themselves are unaware of the Kotlin DSL, and any other tool (let it be another code generator or documentation tool) can use the typings if you provide them.

In this feature request, I would like to ask you if you're open to introducing such typings in your actions. You wouldn't be first - there're already other actions using it: https://github.com/krzema12/github-actions-typing/network/dependents

If your answer is "yes", feel free to either add it yourself, or let me know - me or some of my fellow contributors would be happy to post PRs. We're also open to any kind of questions and feedback.