Enabling CSE encryption for COPY command

[ameent]

With these changes one can write encrypted data to S3 using client side encryption, with a custom symmetric master key, and then use spark-redshift to ingest the data. I have sensitive data ingesting into Redshift and can't use S3-SSE for my data.

The main change was to switch away from WITH CREDENTIALS syntax and explicitly pass iam_role, access_key, etc. parameters so that the end-user can use the "extracopyoptions" to supply their symmetric key.

Usage:

sparkSession.table(name)
      .write
      .format("com.databricks.spark.redshift")
      .option("url", redshiftUrl)
      .option("dbtable", options(REDSHIFT_TABLE_NAME))
      // If the table does not exist, then it will be created. If it exists, then data will be appended to it
      .mode(SaveMode.Append)
      .option("temporary_aws_access_key_id", options(AWS_ACCESS_ID))
      .option("temporary_aws_secret_access_key", options(AWS_SECRET_KEY))
      .option("temporary_aws_session_token", options(AWS_SESSION_TOKEN))
      .option("tempdir", options(REDSHIFT_TEMPORARY_S3_LOCATION))
      // we must encrypt the data when writing to S3, and we have to pass
      // the symmetric encryption key to Redshift so that it can decrypt the data.
      // See http://docs.aws.amazon.com/redshift/latest/dg/c_loading-encrypted-files.html
      .option("extracopyoptions", s"encrypted master_symmetric_key '$encodedSymmetricKey'")
      .save()