[5.x][4.x]: Improve setting amount when adding a donation line item in the CP

[icreatestuff]

What happened?

Description

When adding a donation line item to an order from the control panel there is no option to set the donation amount, which then triggers an error preventing the order from being able to update on save.

Curiously you can set the quantity of donation line items to add, which presumably should only ever be a maximum of 1.

Steps to reproduce

1. Enable donations
2. Create an order
3. Add the donation line item
4. See the error about no Donation Amount set

Expected behavior

Adding a donation line item should allow setting the amount

Actual behavior

No amount field is visible when adding the donation line item, causing the amount to be set to 0 and therefore causing an error

Craft CMS version

Pro 4.13.0

Craft Commerce version

4.7.0

PHP version

8.1.29

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions