http.url based Sampler

[iNikem]

There is a request in java instrumentation repo to filter out spans for specific endpoints, such as healthchecks.

There is also a corresponding specification issue.

Before attempting to submit a specification proposal, I would like to try to create a POC sampler in this repository. It would take a list of url patterns and a delegate sampler. Sampler.shouldSample will then check if passed attributes contain http.url semantic attribute. If they do and that url matches one of the patterns, io.opentelemetry.sdk.trace.samplers.SamplingDecision#DROP will be returned. Otherwise, decision will be delegated to the delegate sampler.

At this moment I don't propose nor plan any auto-configuration support for this sampler.