S3 copy example missing URL-encode

[worpet]

The copySource(String copySource) method requires the source to be URL-encoded. According to the documentation:

The name of the source bucket and key name of the source object, separated by a slash (/). Must be URL-encoded.

In the CopyObject.java example, this is not being done:

aws-doc-sdk-examples/javav2/example_code/s3/src/main/java/com/example/s3/CopyObject.java

Line 64 in 6afd1a3

.copySource(from_bucket + "/" + object_key)

A casual test of the example code will appear to work, but it may fail later when you happen to have a key that contains an unsafe URL character.

Related to aws/aws-sdk-java-v2#1313.