Revise Zipkin tracer provider implementation so it implements the Helidon neutral tracing API

[tjquinno]

Environment Details

• Helidon Version: 4.x
• Helidon SE or Helidon MP
• JDK version:
• OS:
• Docker version (if applicable):

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Problem Description

Currently the Helidon Zipkin tracing provider implementation does not directly implement the Helidon neutral tracing API. It implements our OpenTracing provider implementation which does implement the Helidon tracing API. But users who want to depend only on Zipkin--without also including OpenTracing--cannot use the Helidon API to do so.