[keyserver] Merge fetchAll and fetchByID functions

Summary:
Instead of having two functions: ane which fetches all the entries and one which filters by id, we can have a single one which handles both cases. Additional benefit is that for current-user spec, we don't need to introduce en exception in spec's interface (we don't need to fetch current user by id).

https://linear.app/comm/issue/ENG-4631/migrate-checkstate-from-session-utils-to-a-spec

Depends on D8927

Test Plan: Modify keyserver db and check if the state get fixed.

Reviewers: kamil, bartek, inka

Reviewed By: bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8941