Improvement: Allow for CloudFormationManagedUploadInfrastructure stack to be deployed without a KMS key

[SamPlatek]

Issue #, if available: Issue #801

Description of changes:

Allows a flag or env variable to be set that will cause the stack that is deployed (CloudFormationManagedUploadInfrastructure) to not deploy a KMS key. If the KMS key is not used, SSE will be used for the bucket. The KMS key will still be deployed by default unless the flag/env var is used.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.