create paradox docs and set up jobs to publish the HTML

This is the only module where we don't have HTML docs for the pekko.apache.org site.

The README covers most of what is needed - so there is an argument that adding Paradox based docs is just window dressing.

Start by reviewing the README, which the issue identifies as the main source for the documentation content. Then determine the repository's documentation and publishing entry points for generating Paradox HTML and posting it to pekko.apache.org. Done means this module has HTML documentation on the site and the publishing jobs are configured.

Written by the indexing model from the issue text.