Add (optional) OpenTelemetry + Xray integration (#95) (#96)

This introduces all the necessary code to be able to send traces to
AWS Xray via `tracing-opentelemetry`. It can be optionally enabled
using the `xray` feature defined on this crate.

Also update the README.md with instructions on how to enable and use
this.

Cargo.toml

@@ -24,13 +24,25 @@ path = "src/bin/server.rs"
 async-stream = "0.3.0"
 atoi = "0.3.2"
 bytes = "1"
+rand = "0.8.5"
 structopt = "0.3.14"
 tokio = { version = "1", features = ["full"] }
 tokio-stream = "0.1"
-tracing = "0.1.13"
+tracing = "0.1.34"
 tracing-futures = { version = "0.2.3" }
-tracing-subscriber = "0.2.2"
+tracing-subscriber = { version = "0.3.11", features = ["env-filter"] }
+# Implements the types defined in the OTel spec
+opentelemetry = { version = "0.17.0", optional = true }
+# Integration between the tracing crate and the opentelemetry crate
+tracing-opentelemetry = { version = "0.17.2", optional = true }
+# Provides a "propagator" to pass along an XrayId across services
+opentelemetry-aws = { version = "0.5.0", optional = true }
+# Allows you to send data to the OTel collector
+opentelemetry-otlp = { version = "0.10.0", optional = true }
 
 [dev-dependencies]
 # Enable test-utilities in dev mode only. This is mostly for tests.
 tokio = { version = "1", features = ["test-util"] }
+
+[features]
+otel = ["dep:opentelemetry", "dep:tracing-opentelemetry", "dep:opentelemetry-aws", "dep:opentelemetry-otlp"]