add aws s3 sse config and aws_session_token support

[declan-fitzpatrick]

closes #198, #253, #254 and #261

• 198 - update logic for AWS credentials, and enable optional AWS_SESSION_TOKEN as a variable.

• 253 - updates docker files with python venv

• 254 - fix notification typo

• 261 - allow optional AWS_S3_SSE to be passed in.

• updated docs