Upgrade Hugo and Docsy

[markmandel]

Before we tackle #2706, let's do an update of Hugo and Docsy to the latest versions (and make sure we don't break anything along the way 😃).

Putting these together because they likely will need to be updated at the same time.

Things that are useful:

• Hugo
• Install Hugo
• Where we install Hugo for Agones
• make site-server - this will build and run the site locally so you can test any changes.
• Docsy - this is the template we use for our docs
• Where to put a copy of docsy: https://github.com/googleforgames/agones/tree/main/site/themes/docsy

This is my thoughts on how to upgrade everything:

• Update the install instructions in the Dockerfile linked above to the latest Hugo version.
• Can try running make site-server to see if anything breaks, but if it does, the solution may be to update Docsy.
• Make a copy of a release of Docsy and put it in the linked folder above (we just copy past it - we don't use git submodules)
• Run make site-server, see if it shows any errors.
• Check pages, see if any rendering has broken.

The only thing to also keep an eye on, I had to make this change to our docsy template to update Google Analytics, so we'll want to make sure that that change is kept (it might be that updating Docsy will update this file).