Add gossip notifications / cluster node notifications to geyser

[linuskendall]

Problem

To avoid having lite clients like (https://github.com/blockworks-foundation/lite-rpc) participate in gossip and causing further # of gossip clients increasing we would like to be able to get notifications via geyer on gossip data / gossip updates.

This would be required to replace the getClusterNodes RPC call.

Proposed Solution

Add a geyser notification for gossip update notifications.

[buffalu]

+1

do you need raw gossip stream, what's inserted into table, or just access to the data structures for gossip?

[lijunwangs]

Can you elaborate on the requirements of "gossip data" and "gossip updates"?

[godmodegalactus]

We just need node information for all the nodes in the cluster especially those who will produce blocks during an epoch. Same as information we get by using the method 'getClusterNodes' on Solana Json rpc. We would also like to know epoch stakes for each validator but that is optional. Epoch stakes will be used to recalculate the leader schedule.

[musitdev]

I've created a POC to test the cluster node notification with geyzer in this PR #34618.