Enforce Formatting of md,js,html,yml with Prettier

[cwfitzgerald]

In #6368, we decided not using CI to do this, but we should include this as part of the release process, just to keep tabs on everything.

@ErichDonGubler how do we actually do this locally?

[ErichDonGubler]

I think we could simply:

1. Resurrect Enforce fmt. of *.{md,js,html,yml} with prettier  #6368 or make a new PR with the same history.
2. Move the automated enforcement in CI to a procedure for a human to do.
3. ???
4. Profit.

[cwfitzgerald]

Yeah - my question could be more simply restated as: "how to install and run prettier locally" :)

[ErichDonGubler]

Prettier can be installed with any Node toolchain management. Most users are familiar with npm install -g prettier. I'm partial to volta install prettier, myself, since Volta nicely solves a lot of Node toolchain management headaches.