[self-hosted] add netbird server (#5232)

* Unified NetBird combined server (Management, Signal, Relay, STUN) as a single executable with richer YAML configuration, validation, and defaults.
  * Official Dockerfile/image for single-container deployment.
  * Optional in-process profiling endpoint for diagnostics.
  * Multiplexing to route HTTP/gRPC/WebSocket traffic via one port; runtime hooks to inject custom handlers.
* **Chores**
  * Updated deployment scripts, compose files, and reverse-proxy templates to target the combined server; added example configs and getting-started updates.

management/cmd/management_test.go

@@ -30,7 +30,7 @@ func Test_loadMgmtConfig(t *testing.T) {
 		t.Fatalf("failed to create config: %s", err)
 	}
 
-	cfg, err := loadMgmtConfig(context.Background(), tmpFile)
+	cfg, err := LoadMgmtConfig(context.Background(), tmpFile)
 	if err != nil {
 		t.Fatalf("failed to load management config: %s", err)
 	}