Remove Kafka 2.0 plugin and standardize on Kafka 3.x ingestion

[xiangfu0]

This PR removes the Kafka 2.0 stream ingestion plugin and migrates remaining Kafka realtime configs and references to Kafka 3.x. It also adds Kafka 3.x server/producer support and preserves backward compatibility by remapping old kafka20 class names to kafka30.

• Remove pinot-kafka-2.0 module and packaging references
• Switch default/quickstart configs, Helm/Docker examples, and UI templates to kafka30 factory
• Add kafka30 KafkaDataServerStartable and KafkaDataProducer plus ServiceLoader entry
• Map legacy kafka2/kafka20 classes to kafka30 in PluginManager with tests
• Align Kafka client versions to Kafka 3

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.14%. Comparing base (0a951fa) to head (c6c4c5c).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
...tream/kafka30/server/KafkaDataServerStartable.java	0.00%	6 Missing ⚠️
...lugin/stream/kafka30/server/KafkaDataProducer.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #17602      +/-   ##
============================================
+ Coverage     63.11%   63.14%   +0.03%     
+ Complexity     1478     1474       -4     
============================================
  Files          3173     3168       -5     
  Lines        189915   189640     -275     
  Branches      29064    29024      -40     
============================================
- Hits         119872   119756     -116     
+ Misses        60711    60572     -139     
+ Partials       9332     9312      -20     

Flag	Coverage Δ
custom-integration1	?
integration	0.00% <ø> (-100.00%)	⬇️
integration1	?
integration2	0.00% <ø> (ø)
java-11	63.13% <50.00%> (-36.87%)	⬇️
java-21	63.11% <50.00%> (+<0.01%)	⬆️
temurin	63.14% <50.00%> (+0.03%)	⬆️
unittests	63.14% <50.00%> (+0.03%)	⬆️
unittests1	55.51% <100.00%> (+0.02%)	⬆️
unittests2	33.98% <50.00%> (-0.03%)	⬇️

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[Jackie-Jiang]

Should we consider keeping Kafka 2.0 support, but treat it as deprecated, i.e. no more support/fix for it?
Is there a strong reason why we want to remove the code?

[xiangfu0]

Should we consider keeping Kafka 2.0 support, but treat it as deprecated, i.e. no more support/fix for it? Is there a strong reason why we want to remove the code?

Mainly increased binary size for the distribution and potential future vulnerabilities