Don't normalize the '-' character in HTTP header names

[mateuszrzeszutek]

Implements open-telemetry/semantic-conventions#369

[laurit]

Same pattern is used in

opentelemetry-java-instrumentation/instrumentation-api-semconv/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/messaging/CapturedMessageHeadersUtil.java

Line 33 in 5d6e322

String key = "messaging.header." + headerName.replace('-', '_');

and

opentelemetry-java-instrumentation/instrumentation/servlet/servlet-common/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/ServletRequestParametersExtractor.java

Line 80 in 5d6e322

String key = "servlet.request.parameter." + parameterName.replace('-', '_');

[mateuszrzeszutek]

I'll make the same change for the server parameters feature; the messaging headers will need to be changed anyway when we start working on the messaging semconv.