feat: Option to execute only UpdateFunctionCode #497

Description

I would like to request a feature to add an option that only executes UpdateFunctionCode and skips UpdateFunctionConfiguration when deploying Lambda functions.

Use Case

When using Infrastructure as Code tools like Terraform to manage all Lambda configuration settings, we want to:

Use Terraform for managing all Lambda configuration
Use lambroll only for code deployment

Currently, to achieve this workflow, we need to either:

Use --ignore to exclude all configuration parameters, which is cumbersome as we need to list every field, or
Run init before each deployment to load the latest configuration

Having a dedicated option to skip UpdateFunctionConfiguration would simplify this workflow.