[Documention] Problem upgrading to DocFx 2.67.0

[Arkatufus]

Based on our experience upgrading to DocFx 2.67.0 earlier this month, we found some problems:

• There might be some CSS changes that interferes with the website footer
• Regression bug that caused some of the code sample snippets to be missing on the website. We need to either wait for the DocFX fix this or change all of our region names to not include dashes (all camel case naming).
• 2.67.0 automatically filters out all internal classes, emitting warnings that these internal class links are missing from the documentation. This is a behavioural change in 2.67.0. We either need to change the XML-DOC to not refer to these internal classes, make the classes public somehow (not recommended), or find a way to switch this default filtering off.

Pros on using the new version:

• Faster build time, from 20+ minutes to 8 minutes
• Support for tabbing, this will be a very useful feature if we want to merge different ways of displaying code into a more compact view. I.e. showing C# and F# code, showing Akka.Hosting and HOCON configuration, etc.