Implement Micrometer integration, with some new abstractions for interceptors and retrofit to MP metrics

[tjquinno]

Resolves #2344.

This is a re-work of #2761 which is now obsolete.

Although many files are affected, I used the first few commits to "chunk" the changes into more reasonably reviewable sections. This PR has evolved in parallel with #2868, including some rebases. The original chunks here are still conceptually valid although some things (like renaming some parameters and classes) appear later in the PR history.

There would have been considerable overlap between MP metrics and Micrometer code. Much of this PR abstracts common behavior out into interfaces and classes in the new service-common/rest and service-common/rest-cdi components and then makes use of those from SE and MP metrics and the Micrometer integration.

PR #2868 abstracted quite a bit of common behavior for interceptors into separate classes and interfaces. This PR:

• Moves the previously-abstracted classes and interfaces into the new common modules, adjusting SE and MP metrics to use them in their new locations.
• Adds Micrometer support using the abstractions.
• Adds doc and examples.

What follows is a much longer description of the work in this PR.

A Possibly Digestible Guided Review

This PR is similar to its earlier incarnation as #2761.

Because the original metrics SE and MP components share so much with their new Micrometer counterparts, this PR combined with the earlier MP-only PR #2868 (which added some abstracting and async support) together have three missions:

• refactor common behavior into the new service-common modules,
• migrate the existing metrics implementation to the new model, and
• build the new implementation for Micrometer on the new model.

Abstractions

Look at the new service-common modules rest and rest-cdi.

service-common/rest

Contains HelidonRestServiceSupport, an abstract superclass for xxxSupport SE classes. It handles config-based customization of the service’s endpoint using web-contextand sets up and configures CORS for the endpoint.

service-common/rest-cdi

• HelidonRestCdiExtension - abstract superclass for CDI extensions which themselves use xxxSupport classes. Helps in creating the underlying xxxSupport service, discarding vetoed types or beans from annotation processing, and more.
• HelidonInterceptor - interface applicable to interceptors in many components - Has several default methods. Provides both “before-only” and “before-and-after” semantics around intercepted invocations.
• InterceptionRunner and its implementation - Not used outside the package, but used by HelidonInterceptor to invoke the distinct behavior in the interceptors and invoke the intercepted Executable. Automatically supports asynchronous JAX-RS endpoints, invoking each interceptor’s post-completion action only after the async work has completed.

Those of you who reviewed the earlier MP-only PR will notice that the public HelidonRestCdiExtension and HelidonInterceptor expose a smaller and simpler surface area than their predecessors from the earlier PR. The runner interface and implementation are now invisible outside the package.

The evolved metrics components

• metrics/metrics - The SE MetricsSupport class has migrated to use the new abstraction.
• microprofile/metrics - The MP CDI extension is shorter and the interceptors are much simpler (and should be faster, and also honor any removals or adjustments to the annotations that other CDI extensions might have made).

The new integrations/micrometer components

• /micrometer (SE) for the new MicrometerSupport class
• /cdi (MP) for the new extension and interceptors

Other pieces

• Doc - docs/se/metrics and docs/mp/metrics. It seemed best to add the new doc for Micrometer support under the metrics sections, thinking that users might well go there first looking for information on Micrometer.
• Examples - examples/integrations/micrometer/se and …/mp

The Helidon Micrometer implementation largely follows the plan laid out in this gist: https://github.com/oracle/helidon/wiki/Options-for-Micrometer-in-Helidon (see the “short-term” option).

[spericas]

LGTM