Optional `dash` dependencies for headless installs

[z-y-n]

In version 1.2.2 dash and jupyter_dash were added as dependencies which themselves require quite a few further dependencies for the new frontend app.

We see value in having such interactivity, but as mandatory dependencies they make our images a bit bloated for our headless installations of the package. It would be great if they can be specified as extra installs to give users some freedom in terms of the installation footprint 🙏

[tylerflex]

@zeyueN totally agree. I will make the change soon. thanks for raising the issue!

[tylerflex]

@zeyueN I implemented something in this PR: it works for me but we will continue to test a bit before merging it in. Should be live in our next release, likely early next week.

#326

[z-y-n]

Hi @tylerflex, really happy to see such a prompt response. Thanks a lot! 🥇

[tylerflex]

absolutely