[native] update Keyserver selection => to be Keyservers in profile settings

Summary: This was a copy change we discussed in last friday's design sync.

Test Plan: Confirmed that Keyserver selection now says Keyservers

Reviewers: rohan, michal, inka

Reviewed By: inka

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9724