[Woo POS][Cash & Receipts] Add Endpoint to send order confirmation to fluxc

[kidinov]

There is no known documentation so the PHP code should be use:

https://github.com/woocommerce/woocommerce/pull/52050/files

Also ios implementation may help

https://github.com/woocommerce/woocommerce-ios/blob/72e52d401b3675b06f7228a3bd108d0c7bd956e5/Networking/Networking/Remote/ReceiptRemote.swift#L1-L63

[dangermattic]

🚫 Please add a type label (e.g. type: enhancement) and a feature label (e.g. feature: stats) to this issue.