A way to query which config source provides a certain config value

As an application developer or admininistrator, I want to see where my config value is serving from so that I can update the value in the right config source.

The issue mentions no files, tests, or entry points. Start by reviewing the Jakarta Config API and existing configuration-source behavior to determine the query's intended contract. Done should include an agreed way to identify the source of a given configuration value, with documented behavior and tests.

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