Backports: networkx, context cleanup

[jtcohen6]

Backports:

• networkx tight pin for remaining v1.1 patches ([CT-677] [Bug] Downstream models do not run correctly after NetworkX 2.8.1 #5286 (comment))
• docs + code cleanup in Update context README #5334

Let's include both of these in v1.1.1-rc2

[gshank]

I thought 1.1 didn't have the networkx problem?

[jtcohen6]

@gshank It didn't, but we're still using a less-than-ideal method (relative to new approach proposed in #5326).

Per conversation in #5286 (comment):

dbt-core v1.1 is still allowing networkx<3 (since this error didn't occur there). Since we don't feel like we fully understand exactly why the extra iteration step added in v1.1 is working, let's either:

• Backport the change in New ancestor/descendant algo #5326 to 1.1.latest
• Pin v1.1 to a tighter upper bound of networkx

#5286 (comment):

I like pinning 1.1 and not backporting since it's a change that introduces risk. We can add that to the RC2 that we are going to push out soon

[gshank]

Makes sense.