4.x Deprecate Micrometer integration component and add "how to use Micrometer API" content to metrics doc

[tjquinno]

Environment Details

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

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Problem Description

In 3.x Helidon supports integration with Micrometer as a parallel metrics implementation. That integration does not tie in to the main Helidon metrics implementation.

In 4.x the Helidon neutral metrics API is currently implemented using Micrometer. Developers who want to use the native Micrometer API can do so directly and their use of Micrometer fully interoperates with Helidon's.

We should deprecate the 3.x-era integration component in 4.x, remove it in 5, and in 4.x we should rewrite/supplement the metrics doc to describe how developers can use the Micrometer API directly (if they want to).