migrate: Allow migrations to request a check run

This is currently only used by upgrade_repo_v2.

internal/migrations/interface.go

@@ -6,11 +6,16 @@ import (
 	"github.com/restic/restic/internal/restic"
 )
 
+type RepositoryCheckOptions struct {
+}
+
 // Migration implements a data migration.
 type Migration interface {
 	// Check returns true if the migration can be applied to a repo.
 	Check(context.Context, restic.Repository) (bool, error)
 
+	RepoCheckOptions() *RepositoryCheckOptions
+
 	// Apply runs the migration.
 	Apply(context.Context, restic.Repository) error