Add favepay to payment_icons

Why are you adding this icons?

I'm adding/updating this icon(s) because ..

[x] I'm associated with the brand and I've read all the brand icon’s guidelines.

Link to the brand guidelines:

[x] All icons have a corresponding entry in db/payment_icons.yml
[x] I have followed the icon guidelines detailed in the CONTRIBUTING.md file
[x] I have optimized the icon with SVGO
[x] I am confident that all icons are clear and easy to read/understand
[x] I have provided a link to the brand icon’s brand guidelines whenever possible.
[x] I have attached a screenshot comparison with the example icon provided in guidelines
[x] I recognize that if my icon is not approved by the Shopify Partners team it may not receive review nor merger.

If this pull request is not adding new icons, you can remove this checklist.