S3 Assets Deploy should include an option to only deploy if dest doesn't exist

[kierans]

I have a scenario that when I'm provisioning an environment (stage) for the first time (eg: dev, test, prod) I need to upload some dummy assets to an S3 bucket so that some CF scripts can find the files. There's an automated process to regenerate the assets and sync them in the S3 bucket; thus overwriting the dummy assets. These assets have a long TTL and need to outlive the resources that's using them (eg: an EC2 instance)

However when redeploying the stack, the s3deploy.BucketDeployment is overwriting the assets due to the Python Lambda running aws cli sync.

I'd be interested in an option in the CDK that allows the assets to only be sync'd to the destination bucket only if they don't exist.