Add AWS Lambda Layer `Description`

[antonpirker]

It would be great to have a parameter layerDescription that is analogue to the existing layerName parameter and which sets the description of the Lambda layer

Why this is helpful:

We want to add information about what version of the SDK and what version of the Lambda Extension is used inside the Layer. This makes it transparent for users of the AWS Lambda extension what version of the Python/JS SDK is used in their Lambda layer. No it is impossible for users to see what version of the SDK is used in their Lambda functions.