SceneViewHelper.cs

using UnityEngine;
using UnityEditor;

public class SceneViewHelper : Editor
{
    [MenuItem("Custom/Scene View/Match main camera %#M")]
    static void MatchMainCamera()
    {
        var camera = GameObject.FindWithTag("MainCamera");

        if (camera != null)
        {
            SceneView.lastActiveSceneView.AlignViewToObject(camera.transform);
        }
    }
}