Update implementation of AWSFile#copy_to to use S3Object#copy_to API

[hyb175]

Reason

• Better support for special characters
  • According to https://docs.aws.amazon.com/AmazonS3/latest/userguide/object-keys.html, there are some characters, such as + (Plus), that are not necessary to be sanitized but requires special treatment.
  • We have encountered issues with filename containing + fails to copy correctly. S3Object#copy_to appears to handle this already if the target is a S3Object.
• Utilizing the underlying S3Object's API with the same name seems to make more sense

Hope this makes sense and let me know what you think!

[sorentwo]

That was a small fix, very nice! Thanks 👍