Add 'New JupyterGIS Project' option to context menu

[arjxn-py]

Description

Ports jupytercad/JupyterCAD#737

Checklist

• PR has a descriptive title and content.
• PR description contains references to any issues the PR resolves, e.g. Resolves #XXX.
• PR has one of the labels: documentation, bug, enhancement, feature, maintenance
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📚 Documentation preview: https://jupytergis--800.org.readthedocs.build/en/800/
💡 JupyterLite preview: https://jupytergis--800.org.readthedocs.build/en/800/lite

[github-actions]

👈 Launch a Binder on branch arjxn-py/jupytergis/new-jgis-file

[github-actions]

Integration tests report: appsharing.space

[mfisher87]

Dope, great idea! What do you think about using "Project" instead of "File", e.g. "New JupyterGIS Project"?

[arjxn-py]

Thanks for the review, Matt :)

Dope, great idea! What do you think about using "Project" instead of "File", e.g. "New JupyterGIS Project"?

I have no strong opinion on this "File" is to keep the uniformity between jupytercad & jupytergis, but to me "Project" sounds good too

[arjxn-py]

Let's do "Project" as Qgis does the same.

[martinRenou]

Thanks!