Add support for 8 triggers related to Billing

[tlefevre-stripe]

Reviewers

r? cc @stripe/developer-products

Summary

This PR adds support for 8 triggers related to Billing:

• invoice.deleted
• invoice.marked_uncollectible
• invoice.sent
• invoice.voided
• customer.subscription.paused
• customer.subscription.trial_will_end
• invoiceitem.created
• invoiceitem.deleted

[tomer-stripe]

Thanks for this! I think one you get Remi + my comments in we can merge.

[tlefevre-stripe]

Thanks for the review! PTAL.