table: add flows column

[oliver-sanders]

The table view is likely going to be the first recipient of offline data since it has the most obvious pagination system and the closest resemblance to Cylc Reivew.

Once we start displaying historical tasks we will encounter issues with multiple flows as we could end up with duplicate entries for the same cycle/task.

Suggest adding a new column to the table view to represent flows.

For bonus points we could consider hiding this column if only one flow is present in the workflow.

Pull requests welcome!

[oliver-sanders]

The "flow numbers" are available in the flowNums field in GraphQL.

To add this information to the table view:

• Add flowNums into the added/updated section of the TaskProxy part of the table view subscription.
• Add a column to the table and hook it up to the value of node.flowNums.

We might want to consider the best way to represent this information (it is a set of integers).