feat: add source-endpoint-url and dest-endpoint-url as separate parameters

[dmbyte]

There are times where it is necessary to copy between 2 S3 compatible storage devices that require the use of the endpoint-url parameter. Adding distinct source-endpoint-url and destination-endpoint-urls significantly widens potential use-cases.

[seruman]

Hi @dmbyte
I do not think accepting separate endpoint URLs would not help as s5cmd does not support copy on cross cloud environments right now. You may use your disk as pointed here; #595 (comment) ; as a a temporary stage between them.

Duplicate of #529.