Sessions autostart: Handle custom URLs in a generic way

[leafty]

Motivation

Context: supersedes #2242, follow up to #2217 / #2469.

Creating shareable links to autostart sessions which open a specific notebook seems to be a feature Renku users rely on.
However, the current implementation is tied to the specifics of Jupyter Lab (/lab/tree/<path>/<to>/<notebook>.ipynb).

Proposal

We believe we can support the same feature on a broader range of interactive sessions environments (rstudio, etc.) by exposing a new search parameter (customPath?) which would be appended to the session URL.

For Jupyter Notebooks, opening a specific notebook at session start would still be possible by passing ?customPath=/lab/tree/notebook_to_open.ipynb.

Tasks

• Investigate alternative interactive session environments and see if they also use URL paths / search params to open specific notebooks or files.

[lorenzo-cavazzi]

This is similar to #2241
If still relevant for Renku 2.0, we should either consider it in the context of the "Jupyter-free images" pitch or make a dedicated pitch.
I'm closing this issue. Feel free to open a new one if you think there are still reasons to consider a similar functionality that could be a quick UI-only solution