[lib] Make media metadata upload to keyserver optional

Summary:
Part of ENG-8708.

Updated useBlobServiceUpload() to perform keyserver metadata upload only when keyserverOrThreadID is present.

Test Plan: Tested together with other diffs in the stack

Reviewers: kamil, tomek

Reviewed By: kamil, tomek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13280