Fix handling of SSE-C keys when copying unencrypted to encrypted objects or objects with different keys

[ashovlin]

Issue #, if available: #6012, and supersedes #8345

Description of changes: When copying a file that originates in S3, the high level aws s3 commands make a HeadObject call for the file that is being copied.

When using server-side encryption with customer-provided keys (SSE-C), callers can specify the key for the source object(s) --sse-c-copy-source/--sse-c-copy-source-key and/or the destination object (--sse-c/--sse-c-key).

The CLI is incorrectly handling this for S3 -> S3 copies, by applying destination key to the copy source object.

1. Copying an unencrypted object to an encrypted one: aws s3 cp s3://$bucket/file.txt s3://$bucket/ssec-copy-c.txt --sse-c AES256 --sse-c-key $key_1
2. Copying an object with different encryption keys: aws s3 cp s3://$bucket/ssec.txt s3://$bucket/ssec-copy-diff-key.txt --sse-c-copy-source AES256 --sse-c-copy-source-key $key_1 --sse-c AES256 --sse-c-key $key_2

Arguably Incorrect Behavior, Leaving for Backwards Compatibility

I think we're arguably handling S3 -> local copies as well. aws s3 cp s3://$bucket/ssec.txt decrypt.txt --sse-c AES256 --sse-c-key $key_1 works, but I can see a case for applying --sse-c-copy-source/--sse-c-copy-source-key to the object that's originating to S3. But I'm preserving this behavior for backwards compatibility, the updated logic only runs for S3 -> S3 copies.

Manual Testing
I didn't add new integration tests, but manually ran the following

# bucket name and local paths
bucket=""
single_file=""
directory=""
key_1=""
key_2=""

echo "\nLocal -> S3 encrypted"
aws s3 cp $single_file s3://$bucket/ssec.txt --sse-c AES256 --sse-c-key $key_1
aws s3 cp --recursive $directory s3://$bucket/ssec-files --sse-c AES256 --sse-c-key $key_1

echo "\nS3 encrypted -> Local"
aws s3 cp s3://$bucket/ssec.txt decrypt.txt --sse-c AES256 --sse-c-key $key_1
aws s3 cp --recursive s3://$bucket/ssec-files decrypt/ --sse-c AES256 --sse-c-key $key_1

echo "\nS3 encrypted -> S3 Unencrypted"
aws s3 cp s3://$bucket/ssec.txt s3://$bucket/ssec-copy-unencrypted.txt --sse-c-copy-source AES256 --sse-c-copy-source-key $key_1
aws s3 cp --recursive s3://$bucket/ssec-files s3://$bucket/ssec-files-unencrypted --sse-c-copy-source AES256 --sse-c-copy-source-key $key_1

echo "\nS3 encrypted-> S3 encrypted (same key)"
aws s3 cp s3://$bucket/ssec.txt s3://$bucket/ssec-copy-c.txt --sse-c-copy-source AES256 --sse-c-copy-source-key $key_1 --sse-c AES256 --sse-c-key $key_1
aws s3 cp --recursive s3://$bucket/ssec-files s3://$bucket/ssec-files-copy --sse-c-copy-source AES256 --sse-c-copy-source-key $key_1 --sse-c AES256 --sse-c-key $key_1

echo "\nS3 encrypted -> S3 encrypted (different keys)"
aws s3 cp s3://$bucket/ssec.txt s3://$bucket/ssec-copy-diff-key.txt --sse-c-copy-source AES256 --sse-c-copy-source-key $key_1 --sse-c AES256 --sse-c-key $key_2
aws s3 cp --recursive s3://$bucket/ssec-files s3://$bucket/ssec-files-diff-key --sse-c-copy-source AES256 --sse-c-copy-source-key $key_1 --sse-c AES256 --sse-c-key $key_2

echo "\nS3 unencrypted -> S3 encrypted"
aws s3 cp --recursive $directory s3://$bucket/$directory
aws s3 cp s3://$bucket/ssec-copy-unencrypted.txt s3://$bucket/ssec-copy-c.txt --sse-c AES256 --sse-c-key $key_1
aws s3 cp --recursive s3://$bucket/$directory s3://$bucket/ssec-copy-from-s3 --sse-c AES256 --sse-c-key $key_1

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