(aws-lambda-nodejs): ICommandHooks requires all hooks to be implementated

### Reproduction Steps

```
new lambda.NodejsFunction(this, "LambdaFunction", {
bundling: {
commandHooks: {
afterBundling(inputDir: string, outputDir: string): string[] {
return [`echo "hello world"`];
},
},
},
});
```

### What did you expect to happen?

For this to be valid, and the equivalent of defining no commands for `beforeBundling` and `beforeInstall`.

### What actually happened?

`Type '{ afterBundling(inputDir: string, outputDir: string): string[]; }' is missing the following properties from type 'ICommandHooks': beforeBundling, beforeInstall`

### Environment

- **CDK CLI Version :** 1.91.0
- **Framework Version:** 1.91.0
- **Node.js Version:** v14.15.1
- **OS :** macOS Catalina
- **Language (Version):** Typescript (4.2.3)

### Other

Happy to provide a pull-request for this, looks very easy to fix. Unless I'm missing something we can just declare the functions as optional and then default them to the equivalent of `() => []`.

---

This is :bug: Bug Report

Start from the ICommandHooks definition used by NodejsFunction bundling and reproduce the TypeScript error with the afterBundling-only example in the issue. Check the bundling command-hook handling for omitted hooks; done means the example type-checks and missing hooks behave like empty command lists.

Written by the indexing model from the issue text.