fix: don't send empty aggregated metric payloads (backport k237) (#15810)

Co-authored-by: Trevor Whitney <trevorjwhitney@gmail.com>

Author: loki-gh-app[bot]

pkg/pattern/aggregation/push.go

@@ -177,6 +177,9 @@ func (p *Push) buildPayload(ctx context.Context) ([]byte, error) {
 	defer sp.Finish()
 
 	entries := p.entries.reset()
+	if len(entries) == 0 {
+		return nil, nil
+	}
 
 	entriesByStream := make(map[string][]logproto.Entry)
 	for _, e := range entries {
@@ -219,6 +222,10 @@ func (p *Push) buildPayload(ctx context.Context) ([]byte, error) {
 		}
 	}
 
+	if len(streams) == 0 {
+		return nil, nil
+	}
+
 	req := &logproto.PushRequest{
 		Streams: streams,
 	}
@@ -268,6 +275,10 @@ func (p *Push) run(pushPeriod time.Duration) {
 				continue
 			}
 
+			if len(payload) == 0 {
+				continue
+			}
+
 			// We will use a timeout within each attempt to send
 			backoff := backoff.New(context.Background(), *p.backoff)