Adding initial support

[ashr123]

About 1 week ago, FasterXML released Jackson 3.0, so I want to add support for it (i.e. being able to read log4j2.json ext. files.
See https://github.com/FasterXML/jackson/wiki/Jackson-Release-3.0
Closes #3950

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[ppkarwasz]

Hi @ashr123, thanks a lot for the PR!

We can’t merge this into the 2.x branch because 2.x targets Java 8, while Jackson 3 requires Java 17. That version mismatch would break our compatibility guarantees for the 2.x line.

As for the main branch (with a Java 17 baseline) we migrated to Jackson 3 shortly after the 3.0.0 release (see #3701) and we’re actively working toward our own 3.0.0 release.