Improve bug report template by adding notes about testing Holoviews

On discord @maximlt mentions he would like users reporting bugs to figure out if there is also an issue in the underlying HoloViews library.

As this is not documented no user reporting issues would know this. And this requirements leads to lots of questions

- Do you require this additional work from any user or only selected users?
- How would one know how to correctly translate hvPlot code into HoloViews code as this can be done in many ways. And the user might not even know HoloViews.
- How would you want a bug reported where there is a bug in hvPlot but no bug can be identified in HoloViews. Should the user provide a working HoloViews example as part of the hvPlot bug report? Should the user note that he/ she has not been able to come of with a similar buggy HoloViews example?
- How would you want a bug reported where there is a bug in hvPlot and the user can convert this into a HoloViews example that also looks buggy. Should it be reported in both repositories or only the underlying HoloViews repository.
- What should the user do if he/ she after exploring HoloViews is in doubt whether this is fundamentally a hvPlot or HoloViews issue? For example what is a bug to hvPlot (something not working) could be a feature request for HoloViews (something not supported yet).