chore: restore "Donate" links section in control panel

[AprilSylph]

Description

Reverts 1f547d4.

Sadly, it looks like linking to the Sponsor window from the contributors graph no longer works. I thought about just duplicating the links created by FUNDING.yml here instead, but I think I still prefer linking to the repository's Sponsor window, since we can update that without pushing out a new addon version.

Before	After

This is quite a few months overdue if considering when I re-enabled the Sponsor button in this repository... but I was wrestling the question on whether or not I deserve to advertise it, given the level of my open-source work output in those months (and the many months prior). The answer I ultimately arrived at is that it's a silly question to begin with; I will become more motivated to do open-source work as more people give their support for it!

(Plus, I did create the thing to begin with, which is probably worth more than the less-than-a-single-month-of-minimum-wage compensation I earned before having to shutter my donation avenues... right...?)

(Opinions on this topic are relevant to reviewing this pull request, if you have any.)

Testing steps

1. Load the modified addon
2. Open the control panel → Links tab
3. Click the "Sponsor the project" link
   • Expected result: The opened link displays the project README, with the "Sponsor AprilSylph/XKit-Rewritten" window open in front of it

[marcustyphoon]

I think any consideration about whether soliciting donations is or feels inappropriate would only start being relevant if it was, like, putting up a colored banner, or something. Things like this (which, let's be real, no one will find) or like the link you put below that update post on your blog, to me, fall squarely in "making it not literally impossible for users to support the project," which I think is quite far on the appropriate side!