## Issue Addressed
#2325
## Proposed Changes
This pull request changes the behavior of the Peer Manager by including a minimum outbound-only peers requirement. The peer manager will continue querying for peers if this outbound-only target number hasn't been met. Additionally, when peers are being removed, an outbound-only peer will not be disconnected if doing so brings us below the minimum.
## Additional Info
Unit test for heartbeat function tests that disconnection behavior is correct. Continual querying for peers if outbound-only hasn't been met is not directly tested, but indirectly through unit testing of the helper function that counts the number of outbound-only peers.
EDIT: Am concerned about the behavior of ```update_peer_scores```. If we have connected to a peer with a score below the disconnection threshold (-20), then its connection status will remain connected, while its score state will change to disconnected.
```rust
let previous_state = info.score_state();
// Update scores
info.score_update();
Self::handle_score_transitions(
previous_state,
peer_id,
info,
&mut to_ban_peers,
&mut to_unban_peers,
&mut self.events,
&self.log,
);
```
```previous_state``` will be set to Disconnected, and then because ```handle_score_transitions``` only changes connection status for a peer if the state changed, the peer remains connected. Then in the heartbeat code, because we only disconnect healthy peers if we have too many peers, these peers don't get disconnected. I'm not sure realistically how often this scenario would occur, but it might be better to adjust the logic to account for scenarios where the score state implies a connection status different from the current connection status.
Co-authored-by: Kevin Lu <kevlu93@gmail.com>
320a683e72