[lib, web, native] extract getting the keyserver admin

Summary:
This common logic has been exctracted to lib, because I need to use this in yet another place
More context on this part of code: ENG-1707
Related issue: ENG-1700

Test Plan:
Checked that web and native launch and name 'ashoat' is displayed in the chat-thread-ancestors component

Reviewers: jacek, tomek, atul, abosh, ashoat, jon

Reviewed By: tomek, abosh, ashoat

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D4958