Add Prettier config

[piercemorris]

To enable consistent auto-formatting to the repository in order to streamline PRs and development. Prettier should read from the already configured .eslintrc.json file. Prettier plugins are recommended to enable this behaviour.

We could also raise a discussion around current rules if there's capacity.

[Casheeew]

stylistic (which we are already using the ts plugin) also has indentation rules: https://eslint.style/rules/js/indent eol: https://eslint.style/rules/js/eol-last

[jamesmaa]

done

[MarvNC]

Was only enabled for markdown, would be nice to have it for everything else.

[djahandarie]

https://prettier.io/docs/en/integrating-with-linters.html is probably a relevant article if this is the direction we want to go.

We would need to remove all the stylistic stuff in our current eslint. Also need to remove lots of the formatting related stuff in vscode settings, and install properly extensions automatically for it to be smooth for new contributors