Add a setting to enable an Affirm logo on the gateway display name

We offer a similar feature in other branded payment methods. We should add an option to prepend one of the logos from Affirm's logo library to the display name of the payment gateway:

https://businesshub.affirm.com/hc/en-us/articles/4425266541204-Logos-Ban...

This can be combined with an option to only use the logo and ignore the display name (given we cannot simply leave the display name empty).

1. Select list of logo options, defaulting to none, labeled: "Prepend the display name with a logo" (with help text that links to the page)
2. Checkbox labeled: "Hide the display name and just use the logo." (only appearing as an option when a logo is selected)