Un-subscribe all gossip when reverting to finalized sync

[dapplion]

Currently we un-subscribe core topics when going to finalized sync

lodestar/packages/lodestar/src/sync/sync.ts

Lines 193 to 194 in 2ed2e03

	this.logger.warn(`Node sync has fallen behind by ${syncDiff} slots`);
	this.network.unsubscribeGossipCoreTopics();

However we keep subnet subscriptions, which are actually the ones taking the bulk of CPU processing.

• Un-subscribe all gossip when reverting to finalized sync

From #2488

[philknows]

Please investigate @tuyennhv , this may already be completed.

[wemeetagain]

This has not been completed, still a real feature request

[twoeths]

will look into this