[keyserver] upgrade redis to version 7 on docker based keyserver
Summary:
Upgrades docker-based keyserver Redis to version 7
Depends on D12458
Test Plan: Launched docker-based keyserver and successfully performed basic user actions. Tested Redis by setting up a self-hosted keyserver and connecting to it with two different iOS simulators, sending messages live
Reviewers: bartek, varun, ashoat
Reviewed By: ashoat
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D12475