Merge dataframe documentation prior to release of DF48

[timsaucer]

Describe the bug

Right now in the documentation on main we have two entries for API and two entries called DataFrame. We should merge the dataframe documentation, and probably make the rendering page a subpage of the main one.

To Reproduce

Open the repo and run the documentation generator.

Expected behavior

Should be more easy to identify the parts of the documentation the user is interested in.