Automatically update runtime versions when released

[TheEvilSkeleton]

Whenever a new runtime releases, the docs will quickly suggest outdated runtime versions. As the docs grow, so will the difficulty of manually updating each page to reflect the newest runtime version. Perhaps we could set up something that automates the process of updating runtime versions?

[orowith2os]

Maybe we should link to a page containing all of the current runtime versions instead? The issue is, there are many different runtimes, and no easy way to see just them, as things like OBS plugins show under flatpak list --runtime.

What about runtime extensions too?

[razzeee]

I'm not even sure we have versions (other then 20.08 which is a min version for a feature) in the docs right now.

https://github.com/flathub/documentation/pull/48 would change that, but two places aren't too bad and maybe not worth automating it

[bbhtt]

There is no runtime version used anywhere now.