Adopt `MetisModificationFailure` usages to also display success

[FelberMartin]

Problem

The app currently only displays if a MetisModification fails, but not if it was successful. It would be helpful in some cases to show a Snackbar message to the user when a modification is successful (eg for edit, delete, resolve, pin, save)

Suggested next steps

• Adapt MetisModificationFailure to be able to show an optional success message