Update watershed.py to make the function return `labels`

[HaleySchuhl]

For context please see... Associated issues

• #1481

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Branch Coverage	100%	100%
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[HaleySchuhl]

Updated debug image so will update example in docs page tomorrow probably

[annacasto]

Just one comment before approving: I don't think the documentation makes it clear how the labels are/can be used or accessed. For example, it says "These data can always get accessed during a workflow (example below)" but the labels are not accessed in the example. Maybe this is better demonstrated by a tutorial, but I think a small example in the documentation page could help illustrate the functionality.

[HaleySchuhl]

Just one comment before approving: I don't think the documentation makes it clear how the labels are/can be used or accessed. For example, it says "These data can always get accessed during a workflow (example below)" but the labels are not accessed in the example. Maybe this is better demonstrated by a tutorial, but I think a small example in the documentation page could help illustrate the functionality.

Good point, just added~~ Thanks Anna!