[Feature Request]: add option to sync only from DA

[tzdybal]

Implementation ideas

Currently it's not clear if node is syncing only using DA or DA and P2P network and there is no explicit way of configuring this behavior.

There are multiple implementation options:

1. Disable entire P2P comms completely - node would only follow DA, no gossiping, peer discovery, etc.
2. Make "sync mode" configurable - DA or P2P or both. Node would still participate in gossiping, peer discovery, etc.
   1. Node that reads from only DA might (or might not) "serve" data via P2P, to help syncing other nodes via P2P.