[FLINK-25122] [flink-dist] Add variable expansion for FLINK_ENV_JAVA_OPTS

[CodeFerriCode]

What is the purpose of the change

Add variable expansion for FLINK_ENV_JAVA_OPTS, and introduce variable FLINK_LOG_PREFIX in flink to make env.java.opts in the documentation like "-Xlog:gc*:file=${FLINK_LOG_PREFIX}.gc.log" work.

Brief change log

• Add FLINK_ENV_JAVA_OPTS=$(eval echo ${FLINK_ENV_JAVA_OPTS}) before starting the JVM.
• Introduce variable FLINK_LOG_PREFIX, so that env.java.opts value containing this variable can get eval correctly.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

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CI report:

• 0140c2d Azure: SUCCESS

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Automated Checks

Last check on commit 98a1592 (Wed Dec 01 12:35:14 UTC 2021)

Warnings:

• No documentation files were touched! Remember to keep the Flink docs up to date!
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Review Progress

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• ❓ 4. The change fits into the overall [architecture].
• ❓ 5. Overall code [quality] is good.

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