[FLINK-34256][doc] Add a documentation section for minibatch join

[xishuaidelin]

What is the purpose of the change

This pull request add doc for mini-batch join.

Brief change log

Add doc for mini-batch join in Performance Tuning which belongs to table.

Verifying this change

N/A

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? (yes)
• If yes, how is the feature documented? (docs)

[flinkbot]

CI report:

• 0778d0d Azure: SUCCESS

Bot commands

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

[lsyldliu]

@xishuaidelin Thanks for contribution, I left some comments.

[lsyldliu]

LGTM