cancellation source customer + feedback

[rishi-raj-jain]

from the ticket

the merchant requests us to share which customer shared (say "missing features") in their subscription cancellation feedback, i.e. feedback <> customers mapping that's being used to paint the graph.

[emilwidlund]

I think we can achieve this by adding the cancellation reasons to this filter. Adding that capability to the API would be necessary too.

[emilwidlund]

As in, adding that dropdown when Canceled is selected.