Option to pass extra opentelemetry attributes

[hdkshingala]

With opentelemetry-webserver-sdk, is there an option to pass extra OTel attributes similar to how it is done in the nginx plugin, which seems not maintained now: https://github.com/open-telemetry/opentelemetry-cpp-contrib/blob/main/instrumentation/nginx/test/conf/nginx.conf#L22

We want to integrate Nginx with our product https://github.com/fluxninja/aperture and need the OTLP log collector from Nginx