Add integration tests for BlueStyle on a repo

[nickrobinson251]

The tests in tests/blue_style.jl (like in tests/yas_style.jl) isolate the changes made by only the style and not any of the other options (keywords) the style recommends by default.

To do a full fledged integration test (using the full settings BlueStyle recommends), we can adding a repo into the tests and a .JuliaFormatter.toml config to use blue style.

We do this for YAS using Onda.jl: https://github.com/domluna/JuliaFormatter.jl/tree/master/test/files/Onda.jl

(suggested by @domluna #300 (review))

[nickrobinson251]

We may need more of #283 to be completed before this

[domluna]

We may need more of #283 to be completed before this

not necessarily it would just update as we go along

[penelopeysm]

Loads of repos are tested with BlueStyle now in CI. I don't check the exact output but formatting works & is idempotent.