Zanzana: Add server side metrics (#109923)

* Zanzana: Add metrics to server side

* Zanzana: Collect check duration

* add metrics for other methods

pkg/services/authz/zanzana/server/server_write.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"time"
 
 	openfgav1 "github.com/openfga/api/proto/openfga/v1"
 
@@ -15,6 +16,10 @@ func (s *Server) Write(ctx context.Context, req *authzextv1.WriteRequest) (*auth
 	ctx, span := s.tracer.Start(ctx, "server.Write")
 	defer span.End()
 
+	defer func(t time.Time) {
+		s.metrics.requestDurationSeconds.WithLabelValues("server.Write", req.GetNamespace()).Observe(time.Since(t).Seconds())
+	}(time.Now())
+
 	res, err := s.write(ctx, req)
 	if err != nil {
 		s.logger.Error("failed to perform write request", "error", err, "namespace", req.GetNamespace())