docs(testing): document automated testing systems

[ace-n]

I felt like our automated testing docs were a bit light, so I 🦅 took the liberty 🦅 of fleshing them out. 😄

BLOCKED on #347

[grayside]

Thanks for getting this started! I've already got a testing.md file merged in docs, with a focus on contributor instructions on how to run tests.

I figure this content has several paths forward, a couple options I see:

• Rename to delivery.md, with the intent to expand into more deployment architecture content in follow-ups
• Rebase onto the merged testing.md, to explain more about automated testing systems after covering how to run tests

[grayside]

If we're going to merge this in the docs, let's remove future things or hold this in waiting until it's true.

[ace-n]

👍 let's do the latter

[ace-n]

I linked to the (optional) installation-testing directory instead.

I'll include a nightly build trigger (via Terraform) in there, via a separate PR.

[ace-n]

Rebase onto the merged testing.md, to explain more about automated testing systems after covering how to run tests

This was my intent; my preference is to keep everything co-located in one place.

Requesting subsequent review :)

[grayside]

LGTM. I will follow-up to rotate manual testing up and give the doc a top-level heading.