Use neighbors according to heartbeat

[kwek20]

Description

With #1792 IRI will support heartbeat checks for neighbors. We only want to connect to neighbors who (partially) support our milestone range

Motivation

Requesting transactions from neighbors who are known not to have the milestone the tx is in, takes a needless toll on network usage

Requirements

• Modify Neighbor setup to not request transactions we know the neighbor doesn't have
• Keep support for neighbors requesting transactions (Thus not dropping them if we aren't interested)

Open Questions (optional)

• How often do we check this?

[GalRogozinski]

Broadcast it every minute or check what hornet does