[native] Call create / update endpoint

Summary:
Connect the UI with the backend. Allows updating and creating a link.
When a link isn't present, show a random string instead.

Depends on D7881

Test Plan: Check if creating / updating links work.

Reviewers: bartek, kamil, inka

Reviewed By: kamil

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7883