Subscription webhooks moved to v3

TLDR

We are gradually deprecating the subscription webhook (formally known as [purchasable_subscription.](https://developers.intandem.tech/reference/subscription-created)

It will be replaced by a new v3 webhook based on the subscription v3 entity

ETA for end of life: Decmeber 2025.

Notable changes

• The name of the webhook is subscription, instead of purchasable_subscription
• purchasable_uid is now offering_uid
• Added the following properties: offering_type, charged_by, trial_type, next_charge_date. New properties are described here.