Add auto logging of goroutine pid label (#19212)

* Add auto logging of goroutine pid label

This PR uses unsafe to export the hidden runtime_getProfLabel function from the
runtime package and then casts the result to a map[string]string.

We can then interrogate this map to get the pid label from the goroutine allowing
us to log it with any logging request.

Reference #19202

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/log/groutinelabel.go

@@ -0,0 +1,20 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package log
+
+import "unsafe"
+
+//go:linkname runtime_getProfLabel runtime/pprof.runtime_getProfLabel
+func runtime_getProfLabel() unsafe.Pointer // nolint
+
+type labelMap map[string]string
+
+func getGoroutineLabels() map[string]string {
+	l := (*labelMap)(runtime_getProfLabel())
+	if l == nil {
+		return nil
+	}
+	return *l
+}