Cowboy opentelemetry plugin

Add cowboy_otel_h first to your cowboy stream handlers, it will pick up propagated spans to cowboy, and surround the request with a span. Also add cowboy_otel_middleware after your cowboy_router middlewares, it will attach the created span from the stream process in the process executing middlewares and your cowboy handler, so subspans are connected.

    ProtocolOpts = #{
        stream_handlers => [cowboy_otel_h, cowboy_stream_h],
        middlewares => [cowboy_router, cowboy_otel_middleware, cowboy_handler],
        ...
    }

Semantic convention

Goal is to follow https://opentelemetry.io/docs/specs/semconv/http/http-spans/

Tests

FIXME: Add test-suite

Release

FIXME: Add github build
FIXME: Make hex release