Expose STS-related APIs

is a collection of tasks related to allowing access to select Synapse folders via AWS S3 APIs and tools. For example it allow a user to get temporary credentials (STS tokens) to access a folder. This issue is to expose the new APIs in the Python client. See who architected the feature and implemented the back end services. is a representative end user.

See sample Python code that calls the new APIs here: https://github.com/Sage-Bionetworks/synapseDocs/pull/713/files?short_path=82e8674#diff-82e867462b91e301ff6befdfefbabffa