Add generateDefaultAlias flag

[mkavalecz]

AWS Lambda hase a sum code size limit of 75GB. Every new version of a lambda function goes towards this limit. There are multiple cleanup scripts on the internet that can be used to clean old versions of lambda functions, none of which can delete a version when there are aliases set for it. Aliases should generally only be used when we want to preserve a specific version for whatever reason.

This flag makes it possible to NOT generate an alias while uploading, unless one is explicitly set with the tag. The default functionality is unchanged, so it's backwards compatible, it only has effect when configured.