Add Documentation to "Set User Data" Endpoint

[William-McGonagle]

Idea

At this point, we have a ton of endpoints and the number just keeps growing. We need to document all of these endpoints but the only way to do that is to write about each of them. That is where you come in. If you would like to document this endpoint, just comment on the post, and I will assign it to you.

Todo

• [ ] Add an item to the OpenAPI file that shows how to "Set User Data"
• [x] Add a documentation page about "Set User Data"