[FR]: Prevent object overwrites in S3 with s3_sync

[Pryz]

What is the current behavior?

Today s3_sync uses aws s3 cp (https://github.com/aspect-build/rules_aws/blob/main/aws/private/s3_sync.sh#L98) to copy the artifacts over to the S3 bucket.

Describe the feature

When using s3_sync to push releases to S3, it might be beneficial to prevent object overwrites. Now that S3 has pre-condition, it is possible to make sure that overwrites can't happen (see https://docs.aws.amazon.com/AmazonS3/latest/userguide/conditional-writes.html for more details).

Replacing s3 cp by s3api put-object or s3api complete-multipart-upload with --if-none-match "*" would prevent to overwrite artifacts pushed to S3, bringing an additional layer of safety.