Option to abort on scalafix migration failure

[cptwunderlich]

I'm currently trying to get custom scalafix migrations to work with our scala-steward setup.
In the process, I'm doing a lot of tests and I noticed the following:

scala-steward finds my update, tries to apply the migrations, they fail for various reasons, scala-steward moves on.
I now have an open PR with the bumped versions, but without the migrations applied, so it won't build.
Fixing the migrations and re-running scala-steward won't help, bc. the dependency version hasn't changed.
I cannot delete a PR on Github. Even if I close it and delete the source branch, scala-steward sees a closed PR for a given upgrade.
So there is no way to "retry".

It'd be nice to have a config option to tell scala-steward not to open the PR at all, if migrations fail. Or to make specific migrations "mandatory", i.e., their failure will cause no PR to be opened.

[fthomas]

It'd be nice to have a config option to tell scala-steward not to open the PR at all, if migrations fail.

Sounds good to me. We could just throw before this line if result is a Left and the corresponding config option is set. This would abort the whole update and not create a PR.