Add CUB extra path dirs

[ahmedtoumi]

Change Description

• Context: During the preflight ensure step, the full property set is parsed so SASL can be validated. When configs reference a Config Provider, Kafka's AbstractConfig.instantiateConfigProviders is triggered and attempts to load the provider classes.
• Problem: The provider implementation may not be on the CUB classpath, causing preflight to fail before the service starts.
• Workaround: todays two not clean workarounds exists :
  -- Overriding CUB_CLASSPATH like /usr/share/java/cp-base-new/*:PATH_TO_CONFIG_PROVIDER_JARS
  -- Copying the config provider jars inside /usr/share/java/cp-base-new/

check issue #111

• Change: Add CUB_CLASSPATH_DIRS and honor explicit CUB_CLASSPATH so provider JARs can be supplied to the preflight classpath without losing defaults.
• Result: Preflight succeeds when using SASL with config providers, provided the provider JARs are added via CUB_CLASSPATH or CUB_CLASSPATH_DIRS. No behavior change when not using config providers.

Testing

unit tests created at test/test_classpath.py

[Copilot]

Pull Request Overview

This PR adds support for extending the Java CLASSPATH in the CUB (Confluent Utility Belt) to resolve issues with SASL config providers during preflight validation. The change introduces a new CUB_CLASSPATH_DIRS environment variable that allows appending additional directories to the classpath without losing the default base paths.

Key changes:

• Introduces CUB_CLASSPATH_DIRS environment variable with flexible delimiter support (:, ;, ,)
• Adds automatic wildcard normalization for directory paths to include all JARs
• Maintains backward compatibility with existing CUB_CLASSPATH and CUB_EXTRA_CLASSPATH variables

Reviewed Changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

File	Description
confluent/docker_utils/cub.py	Core implementation of classpath building logic with new environment variable support
test/test_classpath.py	Comprehensive unit tests covering various classpath scenarios and edge cases
docs/CHANGELOG.rst	Documents the new feature in the unreleased section
README.md	Adds detailed documentation and usage examples for the new classpath functionality

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[Copilot]

Pull Request Overview

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

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[etech-data]

test localy passes

different use cases handled at _build_classpath (cub.py)