feat: Add support for pprof in coder agent (#1985)

* feat: Allow USR1 signal to start pprof

cli/agent_unix.go

@@ -0,0 +1,38 @@
+//go:build !windows
+
+package cli
+
+import (
+	"context"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"cdr.dev/slog"
+)
+
+func agentStartPPROFOnUSR1(ctx context.Context, logger slog.Logger, pprofAddress string) (srvClose func()) {
+	ctx, cancel := context.WithCancel(ctx)
+
+	usr1 := make(chan os.Signal, 1)
+	signal.Notify(usr1, syscall.SIGUSR1)
+	go func() {
+		defer close(usr1)
+		defer signal.Stop(usr1)
+
+		select {
+		case <-usr1:
+			signal.Stop(usr1)
+			srvClose := serveHandler(ctx, logger, nil, pprofAddress, "pprof")
+			defer srvClose()
+		case <-ctx.Done():
+			return
+		}
+		<-ctx.Done() // Prevent defer close until done.
+	}()
+
+	return func() {
+		cancel()
+		<-usr1 // Wait until usr1 is closed, ensures srvClose was run.
+	}
+}