[keyserver] validate if policies are acknowledged on request

Summary:
Checking acknowledgment before executing responder, on both HTTP and WebSocket endpoints. User will not be able to use the app without accepting policy, because most of the functionalities are disabled (will return an error), we can also disable not only API_RESPONSE socket message, but with current approach we will achieve our goal and maintain keyserver connection under the hood, so after accepting user will be able to use app immediately without waiting for e.g. socket initialization.

Context in ENG-2363.

Test Plan: Check if policies are properly validated on both WebSocket and HTTP request, if any of required acknowledgment is missing client should receive an error.

Reviewers: tomek, atul

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5824