Add circleci step to run Prettier

[barrymcgee]

Done

As we do not use run Prettier on pre-commit, this change is to run it as a build step instead.

QA

• Sanity check code
• Check CircleCI Console?

Question

@nottrobin Do we have a shared config for CircleCI tasks?

[nottrobin]

We don't have a "shared" one, but all our circleci configs do follow a similar pattern:

• They use our canonicalwebteam/dev image
• They split up named jobs - e.g. lint-scss, test-python, test-site etc.

Example

[nottrobin]

So in this case you could have one job called e.g. "check-prettier". And maybe one for "test-site" if you have time.