feat: added checkout session

[Niki2k1]

What kind of change does this PR introduce?

This PR adds sync for the checkout sessions (and line items)

Additional context

I created two new migrations (one for the checkout sessions and one for the line items.

I am not yet using this in production, so I am a little bit cautious. My tests worked fine though.

[jackkru69]

We also need this feature, can someone watch this PR?

[revoks]

This feature is something we urgently need on our side as well.
Would love to see this merged - thanks so much for your work!

[kevcodez]

Thanks for the contribution!

Can you please

• Add the webhooks to the README as supported
• Clarify whether line items are present in webhooks
• Add an appropriate webhook test

[kevcodez]

This should be a single upsert and not one upsert per line item ideally

Are line items sent via the webhook by default? Otherwise the checkout session line items would never be there for a regular webhook

[Niki2k1]

Thank you for the Review.

I inspected a checkout session event and indeed there are no line items, so either I would've to fetch them via the api or ignore them and only sync checkout sessions. What do you think?

For my use-case it would be really nice to have the line items directly when syncing

[kevcodez]

@Niki2k1 yeah makes sense, i think a check session without persisting the line items themselves would not add too much value.

I think it would be best to call stripe.checkout.sessions.listLineItems (and set a high limit of 100) if no line items is provided - we also have an expansion feature that can be used (see expandEntity).

So

• If line items is already present, use expandEntity
• If line items are not present, pull from API using listLineItems