Actix Web OpenTelemetry

OpenTelemetry integration for Actix Web.

Exporter configuration

[actix-web] uses [tokio] as the underlying executor, so exporters should be configured to be non-blocking:

```toml [dependencies]

if exporting to jaeger, use the tokio feature.

opentelemetry-jaeger = { version = "*", features = ["tokio"] }

if exporting to zipkin, use the tokio based reqwest-client feature.

opentelemetry-zipkin = { version = "*", features = ["reqwest-client"], default-features = false }

... ensure the same same for any other exporters

```

Execute client and server example

```console

Run jaeger in background

$ docker run -d -p6831:6831/udp -p6832:6832/udp -p16686:16686 jaegertracing/all-in-one:latest

Run server example with tracing middleware

$ cargo run --example server

(In other tab) Run client example with request tracing

$ cargo run --example client

View spans (see the image below)

$ firefox http://localhost:16686/ ```