Add a loading template for page transitions

[mansona]

Hey @sivakumar-kailasam just to give you a bit of background on this. There are some internal issues with Fastboot/Prember/Glimmer (wasn't able to track down exactly where the issue was) that were preventing this from working before. There is code in there that should allow it to be turned back on (or maybe it was a branch) but if anyone wants to tackle this they need to be extra careful that it's working before we merge the PR 👍

Just a little bit of a "thar be draggons" warning 😂 🐉

[sivakumar-kailasam]

That's a surprise. Wouldn't that have been a big fuss given that this is a common functionality? Or did it have to do with prember?

[locks]

Do we still want to pursue this?

[locks]

Closing!