schemas: add offer_id to invoice_creation notification

[daywalker90]

Also partially reverts f960996 which was not properly rebased

PR #8981 was not properly build upon master where notifications were already derived from schemas.

[cdecker]

Very good, just for my own understanding, why the big documentation change?

[daywalker90]

Best to describe it in a timeline:

• notifications (and hooks) were documented here: https://docs.corelightning.org/docs/event-notifications getting out of sync because they are not generated from anything
• PR lightningd: include offer_id in invoice_creation notification #8981 is opened
• PR that generates documentation for notifications and hooks from schemas is merged. It removed the documenation from https://docs.corelightning.org/docs/event-notifications and generates from schemas to https://docs.corelightning.org/reference/notification-balance_snapshot
• PR lightningd: include offer_id in invoice_creation notification #8981 is merged with an unclean rebase where the old documentation was committed again
• This PR removes the old documentation again and generates the new field documentation/code from our new notification schemas

[cdecker]

Thank you for the explanation, makes sense 👍