#Payments: Upgrade Coinbase payment interface

[gtandersen]

Is your feature request related to a problem? Please describe.
Coinbase has announced an upgrade of their payment system affecting all merchants with a cut-off April 15:

https://help.coinbase.com/en/migrating-to-the-onchain-payment-protocol

After having performed the upgrade, dynamic cryptocurrency payment links (invoices) have disappeared from our payment interface forcing our customers to use the Coinbase service directly while BTC based payments are only possible via a Coinbase wallet.

While we have amended our payment interface in #1546, we may need an alternative payment flow for customers who do not want to set up a Coinbase account.

Describe the solution you'd like
A workaround for this issue would be a method for customers to transfer cryptocurrency manually after initiating a payment similar to bank transfers and cash payments.

After inserting a pending transaction locally we display instructions to the customer on how to transfer the cryptocurrency, which can then be confirmed and activated by staff.

Example of payment modal: