Refactor: Replace validator.js dependency from @tsoa/cli

[luupanu]

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Motivation: we use @tsoa/cli in some of our AWS Lambdas and it happens to import the entirety of validator.js which is 130kB of about just anything, where it's just used for ISO8601 checks in @tsoa/cli.

130kB of unused code is bad in itself – but in general bundling that much extra code makes cold starts in Node.JS lambdas worse.

Potential Problems With The Approach

This only replaces validator.js dependency in @tsoa/cli, not in @tsoa/runtime.

Other than that, validator.js is a CJS package and it's not tree-shakeable no matter how you import it. Once you import it, you get everything.

Test plan

Unit tested the custom function.

[github-actions]

Hello there luupanu 👋

Thank you and congrats 🎉 for opening your first PR on this project.✨

We will review the following PR soon! 👀