Improve single-node testnet support and Arc NetworkConfig/ChainSpec (#6396)

* Arc ChainSpec and NetworkConfig

* Fix release tests

* Fix lint

* Merge remote-tracking branch 'origin/unstable' into single-node-testnet

beacon_node/lighthouse_network/src/service/utils.rs

@@ -30,10 +30,10 @@ pub const MAX_CONNECTIONS_PER_PEER: u32 = 1;
 pub const METADATA_FILENAME: &str = "metadata";
 
 pub struct Context<'a> {
-    pub config: &'a NetworkConfig,
+    pub config: Arc<NetworkConfig>,
     pub enr_fork_id: EnrForkId,
     pub fork_context: Arc<ForkContext>,
-    pub chain_spec: &'a ChainSpec,
+    pub chain_spec: Arc<ChainSpec>,
     pub libp2p_registry: Option<&'a mut Registry>,
 }