Initial designation of code owners

[jameysharp]

We want to make sure every contributor gets some kind of meaningful response in a timely fashion. To that end, this PR configures GitHub to auto-assign somebody to every newly-opened PR.

People must only be added to this file if they've agreed to this obligation. The details of what's expected are listed in the file. I'll only merge this if it's signed off by everyone listed in this initial version.

I've requested review from everyone; please either approve or request to be removed. Or suggest changes, of course; I'd particularly like to know if my description of the expectations aren't clear or don't seem right, or if we should slice up the repository differently.

I considered using the bytecodealliance/cranelift-core and wasmtime-core teams for this, but they have too many people and I wanted to make sure I was getting opt-in from everyone. Eventually I think we should create a few new teams specifically for this purpose, but that requires bytecodealliance org admin rights as far as I can tell, and I wanted to get the general shape of this sorted out before dealing with that.

I'd like to ask some more people to join some of these lists, but for example @itsrainy is out this week so I couldn't check with them.

[pchickey]

I think its worthwhile to break down the /crates further:
I will volunteer for component-macro, component-util, environ, fiber, runtime, test-programs, wasi, wasi-common, wasmtime, wiggle, wit-bindgen

wasi-nn and wasi-threads are maintained by @abrown, I will be a secondary on these in case he is unavailable
winch is @saulecabrera

[jameysharp]

I wanted to limit the number of people in this initial PR so we can start evaluating how well this works for the project as a whole. If Andrew or Saúl would like to make the time commitment described in this file, we can certainly add them later.

Also, keep in mind that I'm not expecting the people in this file to necessarily be the ideal reviewers for the areas covered. Instead they should be people who know who the right reviewer is and, more importantly, can quickly get a response out so a contributor isn't waiting a long time. So it isn't as important to be precise about who's handling which area. I think it's more important to keep the lists simple so it's easy to tell at a glance who might get handed what.

In particular, given that you've volunteered for a third of the directories in /crates, I think you have a good idea who to hand reviews off to for the rest. So if it's alright with you, I'll just add you to the rotation for the whole Wasmtime group and drop the WASI category.

[saulecabrera]

@jameysharp I'm good with the time commitment described in this document and to be added to this list whenever you feel it's convenient. Thanks!

[cfallin]

LGTM for my assignments; I'm hopeful that this leads to better distribution of work!

[elliottt]

Looks good to me!

[fitzgen]

Agreed that we can be more fine-grained, but agreed that it can happen in follow ups.

[jameysharp]

I didn't notice when Pat acked this. Now having signoff from everybody, I'm going to merge this and we'll see how this works out for this project.

@saulecabrera, thanks for offering! Let me get back to you after getting a little experience with how this is going. Assuming it goes well we should discuss expanding it during the Wasmtime and Cranelift meetings.