[FLINK-XXX]FLIP-607: Migrate Flink off end-of-life OkHttp; keep it off the core classpath

[MartijnVisser]

What is the purpose of the change

• Switch flink-kubernetes from okhttp to jdk (the built-in Java HTTP client`
• Update various dependencies
• Add Maven enforcer rules to forbid OkHttp on the classpath

Brief change log

This PR is broken up into multiple commits:

• d1a677a to first move okhttp to jdk
• 1599d96 bumps the Fabric8 client
• ea8f798 bumps OkHttp to a maintained version, for the dependencies that need it and are running in isolated classloaders
• 5912968 to align otel with the OkHttp bump
• 7e10fab to make InfluxDB work with the OkHttp bump
• ee49e4d to add the enforcer rules
• 4872a61 for documentation purposes

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): 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): no
• 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

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• Yes (please specify the tool below)

Generated-by: Claude Code (Claude Opus 4.8)

[flinkbot]

CI report:

• 4872a61 Azure: SUCCESS

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