Scala linter and formatter

[youri-k]

• this pr adds:
• scapegoat as scala linter
• scalafmt as scala formatter
• this also adds these steps to the build pipeline

Steps to test:

• CI should catch everything

Issues:

• fixes Investigate Linter and/or Formatter for Scala #3211

---

- [ ] Updated changelog
- [ ] Updated migration guide if applicable
- [ ] Updated documentation if applicable
- [ ] Needs datastore update after deployment

• Ready for review

[youri-k]

I let the scalafmt run on the code basis and corrected most linter errors or surpressed them for certain methods, so this is a pretty huge change. I think after the tracing store merge would be a good time to merge this change as there are no other open backend prs.

[fm3]

@jstriebel @rschwanhold please have a look at the resulting code style. (1) Do you think it is a good idea to have a formatter in place? And (2), should we change its config?

[fm3]

@youri-k can you explain the differences in the snapshots? What happened here / did you fix bugs in the code? How does the user-facing behavior change? Thanks!

[youri-k]

The changes in the snapshots were necessary because this condition is now checed correctly. Due to this change the annotation snapshot depended on the time between the first and the second call of this route. This time changes from run to run, so it isn't a good idea to check this. The test already implemented a method to replace volatile values, so I added the key tracingTime to be replaced and called it in the specific test. This lead to the changes in the annotation snapshot, where other volatile values are now replaced, too and to the changes in the task snapshot. Regarding the now changed values in the annotation snapshot, I added a check for the annotation id and the skeleton id as they're not volatile in this scenario.
The user-facing doesn't really change except for the fact we may log additional time because of corrected check.

[rschwanhold]

LGTM.
The only thing that we could discuss is if we really don't want to use curly brackets around a method that has only one statement:

override def onNotAuthenticated(implicit request: RequestHeader): Future[Result] =
         Future.successful(Unauthorized(Messages("user.notAuthorised")))

This example is pretty obvious, but another example is:

override def routeRequest(request: RequestHeader): Option[Handler] =
if (request.uri.matches("^(/api/|/data/|/assets/).*$")) {
      super.routeRequest(request)
    } else {
      Some(Action { Ok(views.html.main(conf)) })
    }

[fm3]

LGTM. Please merge only after tracingstore (#3281 )

[youri-k]

@jstriebel Please take a look as well because this would enforce all backend code to correspond to this style.

[jstriebel]

Awesome PR!