build: add recommended config files for VSCode remote development (#30450)

Add some recommended config files to use (as is or as basis) for setting
up [remote development using docker containers][1] with VSCode. This is
an opt-in feature. See `.devcontainer/README.md` for more info.

The configuration can be further tweaked/improved, but is a good
starting point.

[1]: https://code.visualstudio.com/docs/remote/containers

PR Close #30450

.vscode/extensions.json

@@ -8,5 +8,8 @@
     "gkalpak.aio-docs-utils",
     "ms-vscode.vscode-typescript-tslint-plugin",
     "xaver.clang-format",
+    // The following extensions are useful when working on angular.io (i.e. inside the `aio/` directory).
+    //"angular.ng-template",
+    //"dbaeumer.vscode-eslint",
   ],
 }