* feat: update lightpush API to make pubSubTopic optional as per autosharding
* Extract contentFilter and subscriptions out of filter to reuse in relay (#779)
* chore: extract contentFilter outside filter package
* chore: move subscription outside of filter so that it can be modified and reused for relay
* Feat: filter select peer for sharding (#783)
* update selectPeer to support pubsubTopic based selection