Decouple controller from data path even when peer-download feature is not turned on

Today, the realtime servers commit segments by pushing to deep-store via controller. The controller is bypassed only when peer-download feature is turned ON. However, decoupling of controller should be independent of the peer-download feature.

Start by tracing how realtime servers commit segments to deep-store through the controller, then compare that path with the peer-download feature's enabled path. Done means controller decoupling works independently of whether peer-download is turned on, but the issue names no files or tests to begin with.

Written by the indexing model from the issue text.