Tidy formatting of Reqwest errors (#4336)

## Issue Addressed

NA

## Proposed Changes

Implements the `PrettyReqwestError` to wrap a `reqwest::Error` and give nicer `Debug` formatting. It also wraps the `Url` component in a `SensitiveUrl` to avoid leaking sensitive info in logs.

### Before

```
Reqwest(reqwest::Error { kind: Request, url: Url { scheme: "http", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("localhost")), port: Some(9999), path: "/eth/v1/node/version", query: None, fragment: None }, source: hyper::Error(Connect, ConnectError("tcp connect error", Os { code: 61, kind: ConnectionRefused, message: "Connection refused" })) })
```

### After

```
HttpClient(url: http://localhost:9999/, kind: request, detail: error trying to connect: tcp connect error: Connection refused (os error 61))
```

## Additional Info

I've also renamed the `Reqwest` error enum variants to `HttpClient`, to give people a better chance at knowing what's going on. Reqwest is pretty odd and looks like a typo.

I've implemented it in the `eth2` and `execution_layer` crates. This should affect most logs in the VC and EE-related ones in the BN.

I think the last crate that could benefit from the is the `beacon_node/eth1` crate. I haven't updated it in this PR since its error type is not so amenable to it (everything goes into a `String`). I don't have a whole lot of time to jig around with that at the moment and I feel that this PR as it stands is a significant enough improvement to merge on its own. Leaving it as-is is fine for the time being and we can always come back for it later (or implement in-protocol deposits!).

beacon_node/execution_layer/Cargo.toml

@@ -50,3 +50,4 @@ keccak-hash = "0.10.0"
 hash256-std-hasher = "0.15.2"
 triehash = "0.8.4"
 hash-db = "0.15.2"
+pretty_reqwest_error = { path = "../../common/pretty_reqwest_error" }

beacon_node/execution_layer/src/engine_api.rs

@@ -10,6 +10,7 @@ pub use ethers_core::types::Transaction;
 use ethers_core::utils::rlp::{self, Decodable, Rlp};
 use http::deposit_methods::RpcError;
 pub use json_structures::{JsonWithdrawal, TransitionConfigurationV1};
+use pretty_reqwest_error::PrettyReqwestError;
 use reqwest::StatusCode;
 use serde::{Deserialize, Serialize};
 use std::convert::TryFrom;
@@ -32,7 +33,7 @@ pub type PayloadId = [u8; 8];
 
 #[derive(Debug)]
 pub enum Error {
-    Reqwest(reqwest::Error),
+    HttpClient(PrettyReqwestError),
     Auth(auth::Error),
     BadResponse(String),
     RequestFailed(String),
@@ -67,7 +68,7 @@ impl From<reqwest::Error> for Error {
         ) {
             Error::Auth(auth::Error::InvalidToken)
         } else {
-            Error::Reqwest(e)
+            Error::HttpClient(e.into())
         }
     }
 }