[FLINK-38523] Update Pekko to 1.4.0

[mateczagany]

What is the purpose of the change

Upgrade flink-shaded to 21.0 and Pekko to 1.4.0

Brief change log

• Upgrade flink-shaded to 21.0
• Upgrade Pekko and Netty to newer versions
• Upgrade all other dependencies affected by the upgrade of flink-shaded

Verifying this change

Integration and end-to-end tests should cover this

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

• Dependencies (does it add or upgrade a dependency): yes
• 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): yes
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: yes
• 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

[flinkbot]

CI report:

• 3da8d29 Azure: FAILURE

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