Suggest a free and open source IDE for contributors

[pdurbin]

Contributors are welcome to use whatever IDE or text editor they wish, of course, but I'd like to propose that pick a free and open source one to mention in the README (and CONTRIBUTING) file. That way they can contribute without financial cost. This is why we suggest Netbeans for the backend: "Developers may use any editor or IDE. We recommend NetBeans because it is free, works cross platform..." -- https://guides.dataverse.org/en/5.13/developers/dev-environment.html#install-netbeans-or-maven

For the frontend, so far I've had good luck with Visual Studio Code: https://code.visualstudio.com

Assuming we decide on VS Code, we could also suggest some extensions:

• run Vitest tests individually: https://marketplace.visualstudio.com/items?itemName=ZixuanChen.vitest-explorer
• ...