chore: update deps and require npm@7

[erunion]

🧰 What's being changed?

• Dropped support for Node 10. It's currently in maintenance mode and is being EOL'd in April.
• Upgrades the local npm usage to require npm@7 for all local development.
• Updates @readme/httpsnippet to the latest release and moves it from being a dep to a peerDep.
• Updates @readme/oas-to-har to the latest release to pull in some fixes w/r/t format: json request bodies. fix(oas-to-har): clean up formatting of raw json bodies api-explorer#1197
• Updates oas to the latest version across both api and httpsnippet-client-api.
  • I added a new getAuth method into Oas (feat: addition of a new getAuth method on the OAS class oas#376) but we've been unable to take advantage of it because we have some semver clases in ReadMe and it's preferring 10.0.0 over 10.2.0 because httpsnippet-client-api had 10.0.0 listed. Incredibly frustrating, but this should let us fully upgrade oas everywhere.
• Moves oas to being a peerDep in httpsnippet-client-api. Since httpsnippet-client-api is a bit more volatile than api, it makes sense to move it to being a peerDep so we can have a bit more leeway when installing it in other other packages and frees us up from having to always do version bumps on oas.

[erunion]

I've started removing these wherever I see them because our ESLint config already runs Prettier, so this is always going to run Prettier on an already prettified codebase.

[domharrington]

LGTM!