Added theme image support to the markdown preview

extensions/github/markdown.css

@@ -0,0 +1,4 @@
+.vscode-dark img[src$=\#gh-light-mode-only],
+.vscode-light img[src$=\#gh-dark-mode-only] {
+    display: none;
+}

extensions/github/package.json

@@ -64,6 +64,9 @@
         "contents": "%welcome.publishWorkspaceFolder%",
         "when": "config.git.enabled && git.state == initialized && workbenchState == workspace && workspaceFolderCount != 0"
       }
+    ],
+    "markdown.previewStyles": [
+      "./markdown.css"
     ]
   },
   "scripts": {