upgrade to libp2p 0.52 (#4431)

## Issue Addressed

Upgrade libp2p to v0.52

## Proposed Changes
- **Workflows**: remove installation of `protoc`
- **Book**: remove installation of `protoc`
- **`Dockerfile`s and `cross`**: remove custom base `Dockerfile` for cross since it's no longer needed. Remove `protoc` from remaining `Dockerfiles`s
- **Upgrade `discv5` to `v0.3.1`:** we have some cool stuff in there: no longer needs `protoc` and faster ip updates on cold start
- **Upgrade `prometheus` to `0.21.0`**, now it no longer needs encoding checks
- **things that look like refactors:** bunch of api types were renamed and need to be accessed in a different (clearer) way
- **Lighthouse network**
	- connection limits is now a behaviour
	- banned peers no longer exist on the swarm level, but at the behaviour level
	- `connection_event_buffer_size` now is handled per connection with a buffer size of 4
	- `mplex` is deprecated and was removed
	- rpc handler now logs the peer to which it belongs

## Additional Info

Tried to keep as much behaviour unchanged as possible. However, there is a great deal of improvements we can do _after_ this upgrade:
- Smart connection limits: Connection limits have been checked only based on numbers, we can now use information about the incoming peer to decide if we want it
- More powerful peer management: Dial attempts from other behaviours can be rejected early
- Incoming connections can be rejected early
- Banning can be returned exclusively to the peer management: We should not get connections to banned peers anymore making use of this
- TCP Nat updates: We might be able to take advantage of confirmed external addresses to check out tcp ports/ips


Co-authored-by: Age Manning <Age@AgeManning.com>
Co-authored-by: Akihito Nakano <sora.akatsuki@gmail.com>

beacon_node/http_metrics/src/metrics.rs

@@ -1,6 +1,6 @@
 use crate::Context;
 use beacon_chain::BeaconChainTypes;
-use lighthouse_metrics::{Encoder, TextEncoder};
+use lighthouse_metrics::TextEncoder;
 use lighthouse_network::prometheus_client::encoding::text::encode;
 use malloc_utils::scrape_allocator_metrics;
 
@@ -9,7 +9,7 @@ pub use lighthouse_metrics::*;
 pub fn gather_prometheus_metrics<T: BeaconChainTypes>(
     ctx: &Context<T>,
 ) -> std::result::Result<String, String> {
-    let mut buffer = vec![];
+    let mut buffer = String::new();
     let encoder = TextEncoder::new();
 
     // There are two categories of metrics:
@@ -50,7 +50,7 @@ pub fn gather_prometheus_metrics<T: BeaconChainTypes>(
     }
 
     encoder
-        .encode(&lighthouse_metrics::gather(), &mut buffer)
+        .encode_utf8(&lighthouse_metrics::gather(), &mut buffer)
         .unwrap();
     // encode gossipsub metrics also if they exist
     if let Some(registry) = ctx.gossipsub_registry.as_ref() {
@@ -59,5 +59,5 @@ pub fn gather_prometheus_metrics<T: BeaconChainTypes>(
         }
     }
 
-    String::from_utf8(buffer).map_err(|e| format!("Failed to encode prometheus info: {:?}", e))
+    Ok(buffer)
 }