[FLINK-38716][docs] Describe the impact of slot.request.max-interval on balanced tasks scheduling.

[RocMarshal]

What is the purpose of the change

[FLINK-38716][docs] Describe the impact of slot.request.max-interval on balanced tasks scheduling.

Brief change log

[FLINK-38716][docs] Describe the impact of slot.request.max-interval on balanced tasks scheduling.

Verifying this change

N.A

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

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

[flinkbot]

CI report:

• 0111e99 Azure: FAILURE

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[davidradl]

To make this clearer, I suggest:

• being explicit as to what you mean by appropriately
• being explicit as to what you mean by sub-optimal and what optimal would look like.
• it would be helpful to describe why increasing slot.request.max-interval can help, and maybe what happens if it is too high.
• Maybe give an example to illustrate the points you are making in the text.