fix: Add std feature to serde to fix linting issues

With a recent breaking update in serde (PR open-telemetry#2976), the `Deserialize`
derive attribute now requires `std` support in order to compile due to
some internal logic inside of serde now being moved behind a feature
gate.

Author: lucamuscat

opentelemetry-proto/Cargo.toml

@@ -58,7 +58,7 @@ prost = { workspace = true, optional = true }
 opentelemetry = { workspace = true }
 opentelemetry_sdk = { workspace = true }
 schemars = { workspace = true, optional = true }
-serde = { workspace = true, optional = true, features = ["serde_derive"] }
+serde = { workspace = true, optional = true, features = ["serde_derive", "std"] }
 serde_json = { workspace = true, optional = true }
 const-hex = { workspace = true, optional = true }
 base64 = { workspace = true, optional = true }