Integrate tracing (#6339)

Tracing Integration
- [reference](5bbf1859e9/projects/project-ideas.md (L297))


  - [x] replace slog & log with tracing throughout the codebase
- [x] implement custom crit log
- [x] make relevant changes in the formatter
- [x] replace sloggers
- [x] re-write SSE logging components

cc: @macladson @eserilev

beacon_node/beacon_chain/src/events.rs

@@ -1,7 +1,7 @@
 pub use eth2::types::{EventKind, SseBlock, SseFinalizedCheckpoint, SseHead};
-use slog::{trace, Logger};
 use tokio::sync::broadcast;
 use tokio::sync::broadcast::{error::SendError, Receiver, Sender};
+use tracing::trace;
 use types::EthSpec;
 
 const DEFAULT_CHANNEL_CAPACITY: usize = 16;
@@ -25,18 +25,14 @@ pub struct ServerSentEventHandler<E: EthSpec> {
     attester_slashing_tx: Sender<EventKind<E>>,
     bls_to_execution_change_tx: Sender<EventKind<E>>,
     block_gossip_tx: Sender<EventKind<E>>,
-    log: Logger,
 }
 
 impl<E: EthSpec> ServerSentEventHandler<E> {
-    pub fn new(log: Logger, capacity_multiplier: usize) -> Self {
-        Self::new_with_capacity(
-            log,
-            capacity_multiplier.saturating_mul(DEFAULT_CHANNEL_CAPACITY),
-        )
+    pub fn new(capacity_multiplier: usize) -> Self {
+        Self::new_with_capacity(capacity_multiplier.saturating_mul(DEFAULT_CHANNEL_CAPACITY))
     }
 
-    pub fn new_with_capacity(log: Logger, capacity: usize) -> Self {
+    pub fn new_with_capacity(capacity: usize) -> Self {
         let (attestation_tx, _) = broadcast::channel(capacity);
         let (single_attestation_tx, _) = broadcast::channel(capacity);
         let (block_tx, _) = broadcast::channel(capacity);
@@ -75,17 +71,15 @@ impl<E: EthSpec> ServerSentEventHandler<E> {
             attester_slashing_tx,
             bls_to_execution_change_tx,
             block_gossip_tx,
-            log,
         }
     }
 
     pub fn register(&self, kind: EventKind<E>) {
         let log_count = |name, count| {
             trace!(
-                self.log,
-                "Registering server-sent event";
-                "kind" => name,
-                "receiver_count" => count
+                kind = name,
+                receiver_count = count,
+                "Registering server-sent event"
             );
         };
         let result = match &kind {
@@ -163,7 +157,7 @@ impl<E: EthSpec> ServerSentEventHandler<E> {
                 .map(|count| log_count("block gossip", count)),
         };
         if let Err(SendError(event)) = result {
-            trace!(self.log, "No receivers registered to listen for event"; "event" => ?event);
+            trace!(?event, "No receivers registered to listen for event");
         }
     }