Complete client timeouts with sdk-default-configuration.json

[jdisanti]

This issue tracks implementation of handling the sdk-default-configuration.json model file for client-side request timeouts.

• Pull in the sdk-default-configuration.json file with the rest of the models during releases
• Add API to select retry mode in SdkConfig and service Config (needs RFC)
• Add ability to override timeout config for individual requests (needs RFC)
• Implement retry mode value resolution logic that occurs at code generation time (multiple/add/override modes that apply to the base config values)
• Implement "auto mode" for timeout value resolution
• Verify if stsRegionalEndpoints and s3UsEast1RegionalEndpoints default configuration values are still relevant after endpoints 2.0, and implement if so