node/peers: basic conn count mgr

[jchappelow]

This adds a basic connection manager that attempts to keep a target connection count. This is useful when a node, such as a validator, has the leader's address in bootnodes, but the leader is down. When the leader is back, it is on the validator to be attempting reconnection with it's known but disconnected peers.

Resolves #1135

2024-12-09 15:17:54.087 [INF] PEERS: Active connections: 0, below target: 20. Initiating new connections.
2024-12-09 15:17:54.088 [WRN] PEERS: Failed to connect to peer 16Uiu2HAkx2kfP117VnYnaQGprgXBoMpjfxGXCpizju3cX7ZUzRhv: failed to dial: failed to dial 16Uiu2HAkx2kfP117VnYnaQGprgXBoMpjfxGXCpizju3cX7ZUzRhv: all dials failed
  * [/ip4/127.0.0.1/tcp/6600] dial backoff

2024-12-09 15:17:55.088 [INF] PEERS: Active connections: 0, below target: 20. Initiating new connections.
2024-12-09 15:17:55.094 [INF] PEERS: Connected to peer (Outbound) 16Uiu2HAkx2kfP117VnYnaQGprgXBoMpjfxGXCpizju3cX7ZUzRhv @ /ip4/127.0.0.1/tcp/6600
2024-12-09 15:17:55.096 [INF] PEERS: Connected to peer 16Uiu2HAkx2kfP117VnYnaQGprgXBoMpjfxGXCpizju3cX7ZUzRhv

2024-12-09 15:17:55.974 [INF] NODE: received Discovery request from 16Uiu2HAkx2kfP117VnYnaQGprgXBoMpjfxGXCpizju3cX7ZUzRhv
2024-12-09 15:17:55.974 [INF] NODE: responded to Discovery request {height=0}
2024-12-09 15:17:55.977 [INF] NODE: processing block proposal {height=1 hash=12745235d053dae93bff86cc2a6cc75f0483cd9bc1e8579e08ed4a5eb15f34d7}
2024-12-09 15:17:55.977 [INF] CONS: Consensus message received {type=block_proposal sender=02c57268fc884fa88425c7e5c19d3af263d1c64dd8b8f3f8c0fb31bb622d1fdab8}