lib/model, lib/versioner: Drive version cleanup from scanner (fixes #6313) (#6693)

This change adds a separate config for the cleanup interval, and runs that cleanup from the main folder loop.

lib/versioner/simple.go

@@ -7,6 +7,7 @@
 package versioner
 
 import (
+	"context"
 	"strconv"
 	"time"
 
@@ -73,3 +74,7 @@ func (v simple) GetVersions() (map[string][]FileVersion, error) {
 func (v simple) Restore(filepath string, versionTime time.Time) error {
 	return restoreFile(v.copyRangeMethod, v.versionsFs, v.folderFs, filepath, versionTime, TagFilename)
 }
+
+func (v simple) Clean(_ context.Context) error {
+	return nil
+}