chore: add CI step for validating contributor READMEs

[Parkreiner]

Closes coder/internal#530

Changes made

• Created top-level test directories for Coder and NataInData (a developer who contributed a module for us in the past)
• Created Go script for validating the structure of each README, while being as granular as possible with any errors for better feedback
• Added CI step for running the script

Notes

• I did a good bit of manual testing, but I am planning to circle back with a follow-up PR to add proper tests for the script functionality. I might push that off until after the majority of the new Registry work is done, though
• Not 100% sold on the structure of the Go directories. That's likely to change as I add more code for validating the modules and templates

[Parkreiner]

This hasn't come up in any of the conversations yet, but I think that it's safe to give developers the freedom to throw whatever they want in the body. We'll just make sure the code always ignores it

[f0ssel]

Mainly just code styling changes, but overall this looks like a great start for validation.

[f0ssel]

If it's not a lot of work, could you drop a screenshot or mock of what the page should looks like with just the bare minimum frontmatter filled out?

[f0ssel]

Are they a partner? Shouldn't this be like community or something?

[Parkreiner]

Yeah, updated the field, and I'll make a quick mockup tomorrow morning.

[f0ssel]

Clean!