Connects the attestation service to network components (#961)

* Sends attestations to the attestation service for processing

* Adds 'attnets' field to local ENR

* Adds ENR bitfield modification logic

* Link attestation service to discovery

- Updates discv5
- Links discover events to discovery
- Support for ENRBitfield

* Adds discovery config params, correct warnings

* Rust fmt fixes

* Correct tests

beacon_node/client/src/builder.rs

@@ -252,7 +252,7 @@ where
     }
 
     /// Immediately starts the networking stack.
-    pub fn network(mut self, config: &mut NetworkConfig) -> Result<Self, String> {
+    pub fn network(mut self, config: &NetworkConfig) -> Result<Self, String> {
         let beacon_chain = self
             .beacon_chain
             .clone()