Add concurrency sync benchmark test (#1224)

This commit added benchmark tests to evaluate performance during
concurrent synchronization with multiple clients. It also improved
benchmark utilities for streamlined setup of servers, clients, and documents.

Author: emplam27

pkg/webhook/client.go

@@ -122,6 +122,11 @@ func (c *Client[Req, Res]) Send(
 	return &res, status, nil
 }
 
+// Close closes the httpClient.
+func (c *Client[Req, Res]) Close() {
+	c.httpClient.CloseIdleConnections()
+}
+
 // buildRequest creates a new HTTP POST request with the appropriate headers.
 func (c *Client[Req, Res]) buildRequest(
 	ctx context.Context,

server/backend/backend.go

@@ -222,6 +222,7 @@ func (b *Backend) Shutdown() error {
 
 	b.Background.Close()
 
+	b.AuthWebhookClient.Close()
 	b.EventWebhookManager.Close()
 
 	if err := b.MsgBroker.Close(); err != nil {

server/backend/webhook/manager.go

@@ -76,6 +76,10 @@ func (m *Manager) Send(ctx context.Context, info types.EventWebhookInfo) error {
 // Close closes the event webhook manager. This will wait for flushing remain debouncing events
 func (m *Manager) Close() {
 	m.limiter.Close()
+
+	// NOTE(hackerwins): It is not good to close the webhook client here
+	// because it is created from outside.
+	m.webhookClient.Close()
 }
 
 // SendWebhook sends the webhook event using the provided client.