Add API documentation for downstream intersphinx

[pllim]

Motivation: To be able to use Sphinx's intersphinx feature to link to your API documentation, such as ipyvuetify.VuetifyTemplate.VuetifyTemplate.

[12rambau]

Hi @pllim I'm working on an update of the documentation that will (hopefully) allow intersphinx to work in #239. Note that the main issue here is that the component are build on the fly from ipyvue when the lib is install so non of them have a docstring per se.

[pllim]

Thanks for the update!