Add a scala formatter

[Asmau1234]

Short description

It would be useful to have a scala formatter on the grid. It would be easier to have a consistent format across the repository.

Steps to reproduce

Actual results (including screenshots)

Expected results (including screenshots)

OS and browser details

[AWare]

Probably worth adding prettier to eslint while we're at it.

[sihil]

We need to figure out how to co-ordinate this with the BBC. We'd want to correct the formatting of all files in a single PR but it would be a major conflict for any other PRs that were in flight. As such we should probably set a day (or weekend?) when we'll do this with an aim to have no inflight PRs at the time.