Updates for integration with dWGS DRS implementation

[gelparsons]

• Adds option to configure FHIR and DRS URLs directly, primarily for internal testing and for when DRS and FHIR do not share the same base URL.
• Converting to/from DRS/HTTPS URLs has been made more flexible to allow for no "api-name" in the base path, in the case where the DRS server is configured directly.
• The dWGS DRS implementation at GEL returns snake_case credentials to S3 buckets. To allow for some flexibility, the client has been changed to be agnostic to how S3 credentials are cased by the DRS server, rather than assume keys are cased exactly as S3 requires.
• DRS uploads now use the newer register-objects endpoint, rather than posting objects directly.
• DRS paths now use "v1" instead of "v1.4".