[native] show loading icon while Comm account being registered via SIWE

Summary:
Context in ENG-2543

Normal flow on my dev environment:

After adding delay to keyserver:

Test Plan: Register via SIWE and check if loading is present (probably simulation of delay on keyserver will be needed)

Reviewers: tomek, atul, ashoat

Reviewed By: ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6068