JPMS and prometheus exporter

[trask]

From @laurit's open-telemetry/opentelemetry-java-instrumentation#5408 (comment)

Note that when using jpms user will need to use --add-modules jdk.httpserver so it would be best if prometheus exporter did not use these classes.

Short of documenting it (e.g. here), wondering (as @laurit mentioned) if we can get rid of the dependency on com.sun.net.httpserver.

org.apache.hc.core5.http.impl.bootstrap.HttpServer in org.apache.httpcomponents.core5:httpcore5 looks reasonable (actively developed, no transitive dependencies, 831 kb, may be worth shading into the prometheus exporter to avoid conflicts, especially since this is in an impl package doesn't give much confidence in API stability).

[anuraaga]

For reference found upstream issue indeed doesn't seem to have been resolved

prometheus/client_java#533

httpcore seems like a reasonable option

[anuraaga]

Though I wonder if providing a real module-info file with a declaration on jdk.httpserver is also an option