fix: use Stripe's Price API for plan-price information (backport #26107)

[mergify]

Stripe has reworked their API to create and manage subscriptions. Initially, we had to connect to the Plans API in order to manage plans (a combination of products and prices), but they've since reworked it to use the new Price API.

The Plans API is still backwards-compatible, but using the new API is a trivial change. I've also changed the fieldname in Subscription Plan to reflect the terms used in the Price API instead.

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This is an automatic backport of pull request #26107 done by Mergify.

[mergify]

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Unmerged paths:
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	both modified:   erpnext/accounts/doctype/subscription_plan/subscription_plan.json
	both modified:   erpnext/erpnext_integrations/stripe_integration.py
	both modified:   erpnext/patches.txt

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