feat: Enable page creation from Jupyter notebook file (*.ipynb)

[Temigo]

Context: This feature is related to the request in https://requarks.canny.io/wiki/p/notebooks-jupyter-or-observable. We use Wiki.js in my research group and it has been great so far! However we rely a lot on Jupyter notebooks (see https://jupyter.org/try for examples), and Wiki.js was lacking the ability to have pages based on a Jupyter notebook.

Example of use case: if we want to demonstrate how to run a library that we wrote, we would typically write a Jupuyter notebook which one could run directly if the .ipynb file is shared (e.g. during a workshop). However we would also want the instructions and code to be available to everyone to read easily, without downloading and running an opaque .ipynb file every time.

Disclaimer: To be clear, this does not allow code execution of the Jupyter notebook cells in the browser, it only renders the notebook nicely (similar to https://nbviewer.jupyter.org/ for example).

Here is the breakdown of the pull request content:

• I created a new Rendering module called ipynb-core, which relies on the npm package notebooksjs (https://github.com/jsvine/notebookjs) to parse the notebook content into HTML. The notebook looks like a regular page with code blocks for the Jupyter notebook cells.

• When creating a new page, I added an option Jupyter in the bottom panel ("Convert from") of editor-modal-editorselect.vue. Clicking on it opens the editor-modal-media to allow the user to select an .*ipynb file.

• .ipynb files can be edited using the code editor (Jupyter notebooks are at their core just a JSON file, this allows one to make minor fixes such as typos if needed without re-uploading a new .ipynb file asset). This required me to change one or two things in editor-code.vue which was forcing the text/html mime type.

• The code also forced a one-to-one correspondence between editors and content types, but the code editor was sufficient for my purpose. I made small changes to allow the same editor to be used by different content types. https://github.com/Requarks/wiki/blob/dev/server/models/pages.js#L294

I am not familiar with Vue.js, so please let me know if I missed something. Thank you !!

[NGPixel]

Thanks for this great PR! I'll try to review it in more details soon, but I'll definitely include it in the upcoming 3.0 release.