This commit switches Hugo to a webhook-based building process, with
support for Github, Gitlab, and Gitea hooks (including local versions of
Gitea) initially. In addition, Hugo-based sites are now intended to be
served under a single volume, with ingress configuration pointing to
sub-paths into the volume.
Documentation for webhook setup and NGINX proxy configuration is still
underway, and will be filled in later.
In addition to changes made when Git repositories update, Hugo is able
to watch for timed changes to content (say, for content that has a
publication date in the future) and build these automatically.
This commit switches from a plain `hugo build` to a `hugo watch` process
to facilitate these use-cases.
By default, a `hugo-build-local@.service` systemd service is included,
for building Hugo-based sites as stored in a local Git repository (as
served by the `git` service), and into a volume (which is intended to be
served by the `nginx-serve-volume` service).
