Add DisconncetedTask

[vbrodsky]

Description

The idea is to improve user experience for long waits. For example, for large data upload tasks, they would have to use code similar to

    task = dataset.create_data_rows(data_rows)
    task.wait_till_done()
    assert task.status == "COMPLETE"

And for long waits the task times out

DisconnectedTask offers an alternative approach

  task = dataset.create_data_rows(data_rows) # record task.id

Some time later

    dt = DisconnectedTask(client, task.uid)
    assert dt.is_completed()
    assert dt.status() == "COMPLETE"
    dt.result()

Currently we just support Task and DataUpsertTask. We will support the ExportTask with this story

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Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Document change (fix typo or modifying any markdown files, code comments or anything in the examples folder only)

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Changes to Core Features

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[mrobers1982]

What's the value add of DisconnectedTask?

The value add is being able to surface a Task by task_id which is provided by TaskFactory.

Personally, I would avoid adding an additional type if it's only purpose is delegation.

[mrobers1982]

This method is redundant as it has the same method parameters as get_task_by_id.

I would not include both as it will only create confusion.

[mrobers1982]

Looks good, I would update the PR title and description to accurately reflect the (updated) implementation.