Create GET /api/stats/blocks propagation endpoint

[shuse2]

Description

Block propagation (api/stats/blocks)

Subscribe to app:network:event event and check for postBlock, increment for every blockId [blockId] +=1, in { 'id1': count, 'id2': count, ... }

Response:

{ // last 300 blocks should be taken into account
    blocks: { <blockid>: count }, 
    averageReceivedBlock: totalCount/numOfBlockIds, // moving average
    connectedPeers: channel.invoke(app:getConnectedPeers).count
}

Motivation

The monitor plugin requires this endpoint to expose how many times block is received on each node.

Acceptance Criteria

• Add unit test to check if the above values are exposed
• Check if the above values are responded by registering to the framework

Additional Information

Related issues: #5216