sbt: allow specifying config as a string

[benwaffle]

I wrote a linter for all of the internal services at my company, as an sbt plugin. Part of the linting process involves running scalafix. It would be nice if I could specify the scalafix configuration as a string instead of a file path. Alternatively, it would be even better if there was some way to run scalafix by calling an internal function and pass the configuration, instead of using the input task like so:

Def.task {
  (Compile / scalafix).toTask(" MyRule MyOtherRule").value
}