Run format apply instead of check.

[ericbottard]

I'm tired of running maven only to realize format is broken.

This PR instead runs the format earlier in the lifecycle. I've used this successfully on other Spring projects.

Now, this has a shortcoming: what if people don't run maven locally before submitting their PR / or before us merging it?
Well, the formatting may differ and become stale, until it gets fixed again with the next well behaved PR.
I still believe this is better than the current frustrating situation.

If you disagree, we can come up with a more advanced setup where CI runs check and developers run apply automatically, having the best of both worlds. Let me know.