feat: Add Feature to Support Copying from External S3 Compatible API and S3 in Cloud Region

[b-eisen]

The current implementation of of s5cmd cp between two s3 buckets invokes the server side copy command. This prohibits users from using s5cmd to copy from an external S3 compatible API (e.g. S3 Compatible API on Snowball Edge devices, minio) to an S3 region (e.g. us-east-1). Users currently have to download the objects and upload in a two step process.

This feature is to enable a --client-copy feature which will allow for copying via the local invoking client, as well as allowing for the use of multiple endpoints, regions, and or credential profiles.