lambda node-18 broke aws-sdk v2

[dchocoboo]

i tried deploying using

• serverless bundle 6
• lambda node18.x

with aws-sdk still using v2 inside my src instead of v3

in the lambda it throws Cannot find module 'aws-sdk'

this is due to deprecation by aws by not including aws-sdk-v2 layers natively

please let us have the option to set aws-sdk as externals so we can include it

[cnuss]

I've added a PR for this here: https://github.com/AnomalyInnovations/serverless-bundle/pull/366

cc: @jayair