[lib][keyserver] Move output entry validators to lib

Summary:
issue: ENG-7818
keyserver/src/responders/responder-validators.test.js will be moved once all validator are moved ENG-8060

Test Plan: flow

Reviewers: kamil, tomek, bartek

Reviewed By: bartek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11938