3.x Inconsistent config prefixes for health-related settings

[tjquinno]

Environment Details

• Helidon Version: 3.x
• Helidon SE or Helidon MP
• JDK version:
• OS:
• Docker version (if applicable):

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Problem Description

The config keys for health-related settings mostly start with health. but for the built-in health checks which themselves are configurable those keys start with helidon.health. (such as helidon.health.diskSpace.thresholdPercent for example).

With the fix in place for #8617 the doc and the code now agree for all the settings, but the inconsistency among the config keys is awkward and confusing.

The settings which start with helidon.health. should be just health. instead. But we'll need to maintain backward compatibility
so we probably need to support both prefix styles for the settings that currently start with helidon.health.. There's an existing utility class that handles deprecated config keys including logging warnings.