Conda forge packages for arvizverse

The new modular structure with the 3 subpackages relies heavily on pip's bundles of optional dependencies. Conda doesn’t allow optional dependencies, but we can have extra packages to “compensate”. For example, matplotlib has matplotlib-base which has not backend and is recommended for downstreams to depend on and matplotlib which includes a recommended backend for users.

We currently have the following conda->pip equivalences

• arviz-base -> arviz-base
• arviz-stats -> arviz-stats[xarray]
• arviz-plots -> arviz-plots

We definitely need to update the dependencies of the already existing arviz package on conda forge. However I am not completely sure to what.

We could also add:

• arviz-stats-core -> arviz-stats
• arviz -> arviz[matplotlib]?
• arviz-plotly -> arviz[plotly] (most relevant for plotly because conda install arviz/arviz-plots plotly won’t work due to webcolors dependency missing)
• arviz-bokeh -> arviz[bokeh]

Having more feedstocks isn't a huge overhead but it takes some resources on conda forge's side and we'll also have to review their recipes every time we make a release even if the review is short.