Separate into packages under the @cdklabs/generative-ai-cdk-constructs namespace

[jstrunk]

I think it would be easier to use the constructs if they were available as individual packages on npm and pypi. Each package would be lighter weight, and they wouldn't fill the namespace with objects that you won't use at that time.

The construct developer experience would be improved if we implement this using an NX monorepo. Builds would be faster as unchanged packages are cached. Each package would be its own AwsCdkConstructLibrary in projenrc. If desired by the developer, the Lambda code could be in subpackages defined in projenrc to manage dependencies and project scaffolding without getting published to npm and pypi.

Autogenerated API documentation would be better. It would match the CDK API docs just by enabling docgen in each construct library package.

It would also provide granular statistics about which constructs are used.