Add a "Note" field to Manual payments

Problem/Motivation

Drupal Commerce now has the "Manual" payment type built into core.

It allows adding a manual payment in the admin area for an order:
/admin/commerce/orders/12345/payments/add

Here it would be great, if the manual payment method type could provide a "Note" field, because manual payments often have special reasons, like for example manual corrections of failed external payments etc.

I think this would be useful for everyone.

If the manual payment is also used client-facing in the checkout, you could also allow users to enter a text, if it makes sense in certain cases.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet