Prettier config: Default config + run once on codebase

[tony]

There's no .prettierrc defined, so when I run formatting, stuff is formatted and it makes the diff very elaborate for only styling purposes.

I think it'd be good to have a config set and run it at least once on the codebase

Trailing commas, lambda function parentheses, newlines after commas (I can't narrow this down to a specific prettier option as of yet)

I have no styling opinion to recommend, but will make a PR to update prettier and run prettier across the codebase so Diffs can be consistent across contributor's systems