Support use staged harness for Dataflow runner v2 job

[Abacn]

Dataflow legacy worker job supports --dataflowWorkerJar pipeline option essentially adding a custom worker jar to the staged files. Actually the same logic (partly) exists in java SDK harness (#6665), but is long broken due to change of artifact names, etc. This change adds it back.

To use it, add custom java SDK harness to runtime class path of your project:

runtimeOnly(group: 'org.apache.beam', name: 'beam-sdks-java-harness', version: "$beam_version")

then run the pipeline with experiments --experiments=use_runner_v2,use_staged_dataflow_worker_jar

example job id: 2025-01-06_12_05_52-7194427615925076100

confirmed that it shows a log

DEBUG 2025-01-06T20:07:45.090268040Z Using staged java harness: beam-sdks-java-harness-2.63.0-SNAPSHOT-Ni9ph3nD4RLvDXNe63bjaKTCqOIHFVnCientEDxi1mM.jar

and a modified line in java sdk harness

Fn Harness started -- modified

Please add a meaningful description for your change here

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