v1.1.3 - Add flag for clearing external cache

Summary

Prior to this version, this would be done by default, however, there are reliability implications if this is done. Mainly that, if there are any 4xx's that happen unexpectedly, we still want the external cache to be able to serve back ups.

As a result, we made this a flag so that this trade off can be done as a choice by end users.

https://hub.docker.com/layers/statsig/statsig-forward-proxy/stable-amd64-1.1.3/images/sha256-7919d5819a149c06aac701d2808e43caee6209d4e9061cc86c1c6b1715750f2c?context=repo