Check global issue templates if none in local repo

[chadwhitacre]

Parent: #22

Problem

Not every repo needs to have its own issue templates defined. In fact, it's probably true that almost all of our repos should be using the global default templates. The issue validator bot/action as it stands today only checks new issues against templates defined in the local repo.

Solution

We should improve the issue validator bot to check local templates if they exist, and global templates otherwise.

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

---

"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[chadwhitacre]

Obsolete now that issue forms is out, we're not doing our own form validation anymore.