Adds an environment variable that can be set to fully skip processing updates. The goal is to set this from the firefox-devtools-mcp to avoid applying updates downloaded in the background when the mcp starts firefox. By default the firefox-devtools-mcp is going to use a temporary profile, so users of the mcp will very often be in the situation where they run the same binary with two different profiles. Differential Revision: https://phabricator.services.mozilla.com/D312722