Support performance trace (#32973)

1. Add a OpenTelemetry-like shim-layer to collect traces
2. Add a simple builtin trace collector and exporter, end users could
download the diagnosis report to get the traces.

This PR's design is quite lightweight, no hard-dependency, and it is
easy to improve or remove. We can try it on gitea.com first to see
whether it works well, and fine tune the details.

---------

Co-authored-by: silverwind <me@silverwind.io>

modules/gtprof/event.go

@@ -0,0 +1,32 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gtprof
+
+type EventConfig struct {
+	attributes []*TraceAttribute
+}
+
+type EventOption interface {
+	applyEvent(*EventConfig)
+}
+
+type applyEventFunc func(*EventConfig)
+
+func (f applyEventFunc) applyEvent(cfg *EventConfig) {
+	f(cfg)
+}
+
+func WithAttributes(attrs ...*TraceAttribute) EventOption {
+	return applyEventFunc(func(cfg *EventConfig) {
+		cfg.attributes = append(cfg.attributes, attrs...)
+	})
+}
+
+func eventConfigFromOptions(options ...EventOption) *EventConfig {
+	cfg := &EventConfig{}
+	for _, opt := range options {
+		opt.applyEvent(cfg)
+	}
+	return cfg
+}