m/pkg/logtree: add Zap and gRPC facades

Change-Id: I37a861edeba9b916e17598da559bd378e494ec35
Reviewed-on: https://review.monogon.dev/c/monogon/+/1486
Reviewed-by: Leopold Schabel <leo@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/pkg/logbuffer/linebuffer.go b/metropolis/pkg/logbuffer/linebuffer.go
index 16f7b1a..92b70e9 100644
--- a/metropolis/pkg/logbuffer/linebuffer.go
+++ b/metropolis/pkg/logbuffer/linebuffer.go
@@ -163,3 +163,7 @@
 	}
 	return nil
 }
+
+func (l *LineBuffer) Sync() error {
+	return nil
+}