http.route is stopped passing to attribute

[sc-yan]

Describe the bug
it'd be rather a change than a bug. in our app, we send otel metrics to datadog. and after a upgrade of "opentelemetry_phoenix" from 1.2 -> 2.0, we found that the span names from HTTP requests are changed from "{http.method} {http.route}" to only ""{http.method}. and this is caused by this commit, which introduced some change and the span name thus is different.

from the spec, the span name should be

 {http.method} {http.route} (when route is available)
{http.method} (when route is not available)

but the commit above stopped passing "http.route" to the attribute.

Expected behavior
we expect "http.route" is passed into attribute.

Additional context
without http.route

with http.route

I created a PR to fix this.

I also have a question. when I log out the span to stdout, I can see the span name is what we want. but if I export it to opentelemetry_exporter, the name would be only {http.method}. I guess there is some process in exporter to change the span name again...?

*SPANS FOR DEBUG*
{span,40098462596871963769597534857057185735,9764691286833948456,
      {tracestate,[]},
      undefined,<<"GET /healthz">>,server,-576460743204758000,
      -576460743168924708,
      {attributes,128,infinity,0,
                  #{'server.address' => <<"localhost">>,'server.port' => 4000,
                    'http.response.status_code' => 200,
                    'client.address' => <<"127.0.0.1">>,
                    'http.request.method' => 'GET',
                    'network.peer.address' => <<"127.0.0.1">>,
                    'network.peer.port' => 54071,'url.path' => <<"/healthz">>,
                    'url.scheme' => http,
                    'user_agent.original' => <<"PostmanRuntime/7.43.0">>,
                    'network.protocol.version' => '1.1',
                    'phoenix.action' => index,
                    'phoenix.plug' =>
                        'Elixir.xxxxxWeb.HealthzController',
                    'http.route' => <<"/healthz">>,
                    'url.template' => <<"/healthz">>}},
      {events,128,128,infinity,0,[]},
      {links,128,128,infinity,0,[]},
      undefined,1,false,
      {instrumentation_scope,<<"opentelemetry_cowboy">>,<<"1.0.0">>,
                             undefined}}