Added deno.json to auto import the MongoDB library

[dfreniche]

While running the JS examples locally in a Jupyter Notebook I'm getting:

TypeError: Could not find a matching package for 'npm:mongodb@6.19.0' in the node_modules directory. Ensure you have all your JSR and npm dependencies listed in your deno.json or package.json, then run deno install. Alternatively, turn on auto-install by specifying "nodeModulesDir": "auto" in your deno.json file. at async :2:25

The fix is to add a deno.json file like:

{
    "nodeModulesDir": "auto",
    "imports": {
        "mongodb": "npm:mongodb@6.19.0"
    }
}