Revert "Remove unassigned event log tags feature"

Revert submission 3400623-remove_unassigned_event_log_tags

Reason for revert: Droidmonitor created revert due to b/383362497. Will be verifying through ABTD before submission.

Reverted changes: /q/submissionid:3400623-remove_unassigned_event_log_tags

Change-Id: I1378364ff5f9c6f09f47d72c104ae603e0d2063a
diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index cd3808c..b9cb076 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -878,7 +878,8 @@
 	eventLogtagsPath := etcPath.Join(ctx, "event-log-tags")
 	builder.Command().Text("mkdir").Flag("-p").Text(etcPath.String())
 	cmd := builder.Command().BuiltTool("merge-event-log-tags").
-		FlagWithArg("-o ", eventLogtagsPath.String())
+		FlagWithArg("-o ", eventLogtagsPath.String()).
+		FlagWithInput("-m ", android.MergedLogtagsPath(ctx))
 
 	for _, path := range android.SortedKeys(logtagsFilePaths) {
 		cmd.Text(path)