On instances, the "SiteSource" (for site config) pretty much copy-pastes the "read POST data" block because it needs to make some decisions based on POST data when handling inbound mail webhooks.

Move the upstream read a little earlier so we can get rid of this. Now that this step is separated and must happen before the profiler, there's no reason not to do it earlier.

POSTed some data across pages without issue, will remove duplicate code in upcoming change.