[keyserver] Create toggle pin messages and updates in parallel

Summary:
Some feedback here was to try to
create the new messages and the updates in parallel by passing two
separate async IIFEs into a Promise.all([...]).

Depends on D8732

Test Plan:
Tested to make sure the new messages and the updates still
occur as before

Reviewers: atul, ginsu, ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8733