Add 'voila' & shiny to list of applications you can open in

### Proposed change

nbgitpuller.link allows explicitly choosing Lab / Notebook / RStudio by default. We should add voila & shiny to this list.

### Alternative options

Continue having users generate the link manually, since you can still specify it in the URL directly.

### Who would use this feature?

People sharing dashboards!

Locate the code that defines the applications available for selection in nbgitpuller.link, using the existing Lab, Notebook, and RStudio options as the entry point. Add voila and shiny to that list, then verify that generated links can select both applications as described in the issue.

Written by the indexing model from the issue text.