Add configuration option to be able to enable uploads even if the consensus paramater `bwscanner_cc` isn't 2

As @gk pointed out, now that we've the metrics DB and grafana dashboards, we might be able to figure out issues with uploads, like #40152 (comment 2891088) and maybe also inflation (team#313) issues.

Instead of just patching a production sbws to force bwscanner_cc as 2, i've thought it'd be better to have an option to switch to uploads (and maybe in the future another option to switch to downloads too) in any bwauth without needing to patch it.