Test and document the ability to upload a custom ProbeInterface file from within HeadstageRhs2116 GUI

[jonnew]

This issue is a starting point for addressing #416. The first thing we need to do, is verify the functionality of using a custom ProbeInterface file for Rhs2116 which has an integrated GUI. We can then use this this infrastructure for creating a GUI for Headstage64.

[jonnew]

Please take some nice screenshots of the GUI with different ProbeInterface files loaded and put those examples in the docs around here: https://open-ephys.github.io/bonsai-onix1-docs/articles/hardware/rhs2116/gui.html#load-probeinterface-file.

[bparks13]

This issue is being closed, as the ability to upload a custom ProbeInterface file has been verified, and the documentation update is at this PR.