Custom hypothesis client

[galachad]

Currently, it's not possible to define a custom js hypothesis client.

It should be possible to set the https://hypothes.is/embed.js to a custom url e.g. https://custom-hypothesis-client.internal/boot.js

https://github.com/quarto-dev/quarto-cli/blob/main/src/resources/formats/html/hypothesis/hypothesis.ejs#L6

Thank you for implementing this.

[mcanouil]

Closing in favour of #4840