docs: added docs for config resolution flow

[thsig]

What this PR does / why we need it:

This should be useful for contributors when debugging config resolution issues or adding features relating to templating (at least to get a high-level orientation and figure out where to start).

[vvagaytsev]

Thank you! 👍
I've left a few comments, please check.

[thsig]

Should be good to go now—I addressed most of the comments (and skipped some of them).

Thanks for reading through this!

[eysi09]

This is great! I see myself looking this up multiple times.

Out of scope for this PR but I'm wondering if we should collect all these in a single place, e.g. a top-level dir called contributing as opposed to co-locating with code.

(I know co-locating is a good thing in general, but maybe high level architectural docs like this are an exception.)

[thsig]

This is great! I see myself looking this up multiple times.

Out of scope for this PR but I'm wondering if we should collect all these in a single place, e.g. a top-level dir called contributing as opposed to co-locating with code.

(I know co-locating is a good thing in general, but maybe high level architectural docs like this are an exception.)

Good idea! I'll do that.

[thsig]

I read this through again and made a couple of edits and clarifications. Should be good to go.

[worldofgeese]

@thsig my only critique is I'm not sure I understand why we're embedding docs in core/src. Shouldn't this be surfaced elsewhere like our actual docs? I could see this as of interest for outside contributing developers. If the docs are inside core/src discoverability seems poor but maybe I'm missing something.

[thsig]

Yeah, makes sense. I've moved these to contributor-docs at the top level (and also added a mention of this directory to the CONTRIBUTING.md guide).

[worldofgeese]

I made one suggestion but this otherwise looks like a fantastic resource for folks looking to understand config resolution.