disable index uploads for prune command

+ modifications of changelog

internal/repository/repository.go

@@ -28,6 +28,7 @@ type Repository struct {
 	keyName string
 	idx     *MasterIndex
 	restic.Cache
+	noAutoIndexUpdate bool
 
 	treePM *packerManager
 	dataPM *packerManager
@@ -45,6 +46,10 @@ func New(be restic.Backend) *Repository {
 	return repo
 }
 
+func (r *Repository) DisableAutoIndexUpdate() {
+	r.noAutoIndexUpdate = true
+}
+
 // Config returns the repository configuration.
 func (r *Repository) Config() restic.Config {
 	return r.cfg