Resolved issue with subgraph configuration

This commit resolves the issues with subgraph configuration, specifically for nodeSpacing and rankSpacing. This commit additionally adds an example graph to the `flowchart.html` to demonstrate this resolution. This commit resolves #3258

demos/flowchart.html

@@ -1540,6 +1540,30 @@
     </pre>
     <hr />
 
+    <pre class="mermaid">
+      ---
+      title: Subgraph nodeSpacing and rankSpacing example
+      ---
+      %%{init:{'flowchart':{'nodeSpacing': 1, 'rankSpacing':'1'}}}%%
+
+      flowchart LR
+      
+      X --> Y
+      
+      subgraph X
+        direction LR
+        A
+        C
+      end
+      
+      subgraph Y
+        direction LR
+        B
+        D
+      end
+    </pre>
+    <hr />
+
     <h1 id="link-clicked">Anchor for "link-clicked" test</h1>
 
     <script type="module">