fix(organisation): disable delete button when active subscription exists

[afsuyadi]

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Changes

Contributes to #7700

1. In DeleteOrganisation.tsx, the button Delete Organisation is disabled only when isLoading is true.
2. However to prevent it being active, we need to add more condition which is related to billing subscription.
3. The component DeleteOrganisation receives Organisation data, which has Subscription property.
4. The interface Subscription itself accepts 2 properties; plan and cancellation_date, for which we can use them as the guarding condition.
5. The Delete Organisation button will remain disabled if plan !== null and cancellation_date === null.

How did you test this code?

1. In local, it's quite difficult for me to find the Billing tab under Organisation Settings and make sure both of the condition has disabled Delete Organisation button, though I can see it in the deployed flagsmith app (https://app.flagsmith.com/).
2. To navigate through this, I use Python Shell to manipulate the database's data, and console.log to see the manipulated value of plan and cancellation_date.

Before changes:
Screencast from 18-06-26 08:44:50.webm

Input for python shell:

from organisations.models import Subscription
sub = Subscription.objects.first()
sub.plan = 'startup'
sub.cancellation_date = None
sub.save()
print(sub.id, sub.plan, sub.cancellation_date)

Input for console.log:

{console.log(
          organisation.subscription.plan,
          organisation.subscription.cancellation_date,
        )}

Output of python shell:

Output of console.log:
Screencast from 18-06-26 09:11:24.webm

[vercel]

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[Zaimwa9]

Thanks for the contribution. We'll need to be more precise to not block free customers to delete their organization

[Zaimwa9]

This would disable the button for all free accounts. We might want to use the planName directly, something like:
Utils.getPlanName(organisation.subscription?.plan ?? '') !== planNames.free && !organisation.subscription?.cancellation_date

[afsuyadi]

I see. I just knew that planNames variable exists. Thanks for the additional info.