Is there a pull request template that does this?
Edit: I was worried about possibly needing to change license. For now I will just use a permissive license. The situation is made seemingly complicated by the possible need to use copylefted images, combined with the possible need for using server code (which shouldn’t use creative commons) in addition to the static html. I would rather deal with including parts with different licenses (probably not as complicated as I initially thought) instead of contributor license agreements.
Edit 2: Also, license enforcement is not very important for my project.
Edit 3: Now I’m using creative commons zero and making the repo comply with https://reuse.software/
What is the need for this?
Some GPL projects do it. If you find someone infringing, it’s easier to sue them if you have one copywrite holder instead of 100.
Generally the only groups I would maybe sign such a CLA in regard to the GPL is: the FSF and the Linux Foundation. Anybody else (especially individuals I don’t know) I wouldn’t sign any CLA unless my contribution is like a 1 off, trivial patch.