Use MediaType accept header parser (#4216)

## Issue Addressed

#3510 

## Proposed Changes

- Replace mime with MediaTypeList
- Remove parse_accept fn as MediaTypeList does it built-in
- Get the supported media type of the highest q-factor in a single list iteration without sorting

## Additional Info

I have addressed the suggested changes in previous [PR](https://github.com/sigp/lighthouse/pull/3520#discussion_r959048633)

common/eth2/Cargo.toml

@@ -10,7 +10,7 @@ edition = "2021"
 serde = { version = "1.0.116", features = ["derive"] }
 serde_json = "1.0.58"
 types = { path = "../../consensus/types" }
-reqwest = { version = "0.11.0", features = ["json","stream"] }
+reqwest = { version = "0.11.0", features = ["json", "stream"] }
 lighthouse_network = { path = "../../beacon_node/lighthouse_network" }
 proto_array = { path = "../../consensus/proto_array", optional = true }
 ethereum_serde_utils = "0.5.0"
@@ -26,7 +26,7 @@ futures-util = "0.3.8"
 futures = "0.3.8"
 store = { path = "../../beacon_node/store", optional = true }
 slashing_protection = { path = "../../validator_client/slashing_protection", optional = true }
-mime = "0.3.16"
+mediatype = "0.19.13"
 
 [target.'cfg(target_os = "linux")'.dependencies]
 psutil = { version = "3.2.2", optional = true }
@@ -34,4 +34,10 @@ procinfo = { version = "0.4.2", optional = true }
 
 [features]
 default = ["lighthouse"]
-lighthouse = ["proto_array", "psutil", "procinfo", "store", "slashing_protection"]
+lighthouse = [
+    "proto_array",
+    "psutil",
+    "procinfo",
+    "store",
+    "slashing_protection",
+]