Add SDK methods for individual multipart upload operations

[nickles-lee]

Changes

• Adds SDK methods for making individual calls to the individual endpoints of the preview implementation of multipart file uploads
• Adds groundwork for future changes that will support switching which specific file transfer backend is used for each request
• Auto-regeneration of the SDK

Planned additional work

• SDK methods will be added that make multipart uploads more ergonomic & user-friendly

Tests

• [✅] make test run locally
• [✅] make fmt applied
• [🔁] relevant integration tests applied

Integration tests will be run when the backend is ready

Merge-hold

We expect minor changes to occur before the backend is ready. This SDK change must not be merged before final changes there are merged.