[CHANGE] Hypothes.is via publisher file

[Rob Beezer]

We have long enabled Hypothes.is as a third-party annotation tool for readers of
your HTML output. I've never been a big fan, so it has always been labeled
"experimental", and controlled with a string parameter.

Not anymore, it is now enabled properly with a publisher file entry. (My
opinion hasn't changed, but it seems to be a feature folks like to use.)

Subsection 45.5.5: HTML Annotation
https://pretextbook.org/doc/guide/html/publication-file-online.html#online-annotation

Rob