Add a right-side toc with "On this page" information when support to that feature is added

[ignacioct]

It will be eventually be supported as a theme option (issue os sphinx referencing it). If not, it would require CSSing it out, or picking another base theme. Pytorch-lighting is able to do this in their docs

This concept is called local_toc.

[dvsrepo]

we can close this