Pull upstream roots/trellis updates

[SteelWagstaff]

We've decided to update Trellis on a quarterly basis. That involves reviewing and merging desired upstream changes to this repository AND our infra repositories.

Notes

In the past, we occasionally merged upstream improvements (see https://docs.pressbooks.org/local-development/windows/#updating-trellis-bedrock for instructions on pulling in upstream changes). Ned did in June 2018: #18, Dac did a few occasions: #19 + #23 + #25. Phil also merged in past: https://github.com/pressbooks/client-infrastructure/commit/8edbb5f7c3017bde6fb4df39f6288c6cc0f05647. Haven’t done for nearly 2 years. Our project is currently 479 commits behind roots:master

[cmurtagh]

The trellis-updates branch now creates working vagrant local install with PHP 7.4, composer 2.1.9, Ubuntu 20.04 when used with the upstream-updates.