Added support for S3 Client Side Encryption (S3 CSE)

[sam33rch]

This commit adds S3 Client Side Encryption support to spark-redshfit library that allows
full end-to-end data encryption over network for read/write operations.

[danielsan]

This is a good one

[ghost]

Agreed. We need this PR merged

[dedgsus]

Another +1. Super useful feature.

[guruswan]

+1. Very useful feature.

[szsiddiq]

+1 This is a great feature - what's keeping it from being merged?

[twwildey]

+1 for this feature!

[rumeshkrish]

Would it possible to add support for KMS_KEY_ID option in UNLOAD command ?

Documentation : https://docs.aws.amazon.com/redshift/latest/dg/t_unloading_encrypted_files.html

Example:

    unload ('select venuename, venuecity from venue')
    to 's3://mybucket/encrypted/venue_' 
    iam_role 'arn:aws:iam::0123456789012:role/MyRedshiftRole'
    KMS_KEY_ID '1234abcd-12ab-34cd-56ef-1234567890ab'
    encrypted;