Lazy load avatar images (#32051) (#32063)

Backport #32051 by @hiifong

Before:

https://github.com/user-attachments/assets/7b1681ba-4781-432a-ae20-c07e94c1dbb6

After:

https://github.com/user-attachments/assets/5154e160-e22c-460e-b0d9-28768486c178

Co-authored-by: hiifong <i@hiif.ong>

modules/templates/util_avatar.go

@@ -34,7 +34,7 @@ func AvatarHTML(src string, size int, class, name string) template.HTML {
 		name = "avatar"
 	}
 
-	return template.HTML(`<img class="` + class + `" src="` + src + `" title="` + html.EscapeString(name) + `" width="` + sizeStr + `" height="` + sizeStr + `"/>`)
+	return template.HTML(`<img loading="lazy" class="` + class + `" src="` + src + `" title="` + html.EscapeString(name) + `" width="` + sizeStr + `" height="` + sizeStr + `"/>`)
 }
 
 // Avatar renders user avatars. args: user, size (int), class (string)