The data-format changed in 2019.
The field `amount_msat` was renamed to `msat`
(See 2907e430d5)
The data-format changed again in november 2023.
The content of the field `amount_msat` was changed.
It was a string `"1000msat"` and became a number `1000`.
(See 0b23133ab2)
The current documentation still mentions the data-format before
2907e430d5.
I've updated the docs to reflect the latest changes.
I've also incluced a short mention of 0b23133ab2 to help help
developers create plugins that work both pre 23.11 and post 23.11.
