[lib][native] Rename uploadBlob to performHTTPMultipartUpload

Summary:
Follow-up to this diff comment. The new name avoids ambiguity with blob service uploads.

(I opted for Multipart instead of MultiPart after a quick Google seemed to show that the former is preferred.)

Test Plan: Flow

Reviewers: tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D11703