Support maxColumnsToMerge in supervisor tuningConfig

[georgew5656]

The StreamAppenderator already supports using maxColumnsToMerge from tuningConfig, the only thing preventing this property from being used is the supervisor/streaming task specs not supporting it.

It would be nice if we could automatically set the value like in MSQE but for now, just let the user specify the value (defaults to -1 which is current behavior).

Release note

• add new supervisor tuningConfig property (maxColumnsToMerge)

Key changed/added classes in this PR

• SeekableStreamIndexTaskTuningConfig

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• a release note entry in the PR description.
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• been tested in a test Druid cluster.

[georgew5656]

the failing unit test seems to be unrelated, so i'm merging this