Feature request: Allow setting a custom S3 client when using LargeMessageHandling

[qtdzz]

Is your feature request related to a problem? Please describe.
Currently the large message handler uses default AmazonS3 client to download client. It means the lambda execution IAM role must have S3 read permissions. The problem is when the S3 bucket is owned by another owner, they provide us the access via an IAM role and ask us to assume that role to read S3 content. Right now, we can't pass a custom S3 client (with assumed credentials) into the LargeMessageHandler.

Describe the solution you'd like
Be able to provide a custom AmazonS3 client for large message handling

[pankajagrawal16]

Thanks for opening the issue @qtdzz . Makes sense, we can probably provide an ability to pass custom s3 client as well.

[pankajagrawal16]

Released as part of https://github.com/awslabs/aws-lambda-powertools-java/releases/tag/v1.8.0