[lib][web][native] Create defaultKeyserverInfo

Summary:
issue: https://linear.app/comm/issue/ENG-6299/save-new-keyserver-on-set-new-session
I will need this value in yet another place so I think it makes sense to extrac it

Test Plan: Tested that add it's still possible to add a keyserver, and the entry looks like it did before

Reviewers: ginsu, michal, kamil

Reviewed By: ginsu, michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10484