Add Flox environment, bump Hugo to 0.110.0 (#668)

# Summary

The "version" of docsy that we use is generating the issue described in
#639 with the latest versions of `hugo`. According to my tests the
latest working version of `hugo` is
[v0.110.0](https://github.com/gohugoio/hugo/releases/tag/v0.110.0).

In addition to specifying the latest working version of `hugo` in the
docs to contribute, I am also adding an [environment with
flox](https://flox.dev/docs/tutorials/sharing-environments/#sharing-environments-with-files).
See also related discussion in #637.

Merging this PR fixes #639. However, we may also want to discuss whether
to [migrate docsy from git submodules to hugo
modules](https://www.docsy.dev/docs/updating/convert-site-to-module/) so
the latest version of both `hugo` and `docsy` can be used.

---

**Related issue :**
#639

.flox/.gitignore

@@ -0,0 +1,4 @@
+run/
+cache/
+lib/
+log/

.flox/env.json

@@ -0,0 +1,4 @@
+{
+  "name": "EGI-documentation",
+  "version": 1
+}