Use CCF CI container in VSCode `.devcontainer.json` (#3874)

.devcontainer/devcontainer.json

@@ -1,7 +1,7 @@
 {
   "name": "Sample Development Environment for CCF",
   "context": "..",
-  "image": "mcr.microsoft.com/ccf/app/dev:lts-devcontainer",
+  "image": "ccfmsrc.azurecr.io/ccf/ci/sgx:oe-0.17.7-1",
   "runArgs": [],
   "extensions": ["ms-vscode.cpptools", "ms-python.python"]
 }