refactor(host_network): extract NetworkManager as a reusable component (#183)

The NetworkManager logic was implemented directly into the `HaClusterTopology`, which wasn't directly its concern and prevented us from being able to reuse that NetworkManaager implementations in the future for a different Topology.

* Extract a `NetworkManager` trait
* Implement a `OpenShiftNmStateNetworkManager` for `NetworkManager`
* Dynamically instantiate the NetworkManager in the Topology to delegate calls to it

Reviewed-on: #183
Reviewed-by: johnride <jg@nationtech.io>

examples/opnsense/src/main.rs

@@ -1,6 +1,6 @@
 use std::{
     net::{IpAddr, Ipv4Addr},
-    sync::Arc,
+    sync::{Arc, OnceLock},
 };
 
 use brocade::BrocadeOptions;
@@ -79,6 +79,7 @@ async fn main() {
         },
         workers: vec![],
         switch_client: switch_client.clone(),
+        network_manager: OnceLock::new(),
     };
 
     let inventory = Inventory {