[FLINK-38211][table-planner] Refactor explain for MultiJoin

[gustavodemorais]

What is the purpose of the change

It'd be useful to have some changes to the explain to make debugging and looking at the job graph easier:

• Add inputUniqueKeys
• Add commonJoinKey
• Add names instead of indices for joinFilter and joinConditions
• Remove joinAttributeMap since it's not easily readable and really long

Brief change log

• Refactor explain in physical node
• Update tests accordingly

Verifying this change

Plan and restore tests updated (this is ok because the operator is in an experimental state)

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)

[flinkbot]

CI report:

• e0510eb Azure: FAILURE

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• @flinkbot run azure re-run the last Azure build

[davidradl]

@gustavodemorais looks like a planner test is failing in the are you have changed.