resolve warnings about casing in Dockerfiles

[jameslamb]

I've been seeing this build warning in logs here:

 2 warnings found (use --debug to expand):
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 37)
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 70)

(example build link)

That comes from BuildKit's build checks (https://docs.docker.com/reference/build-checks/). Details on that specific warning: https://docs.docker.com/reference/build-checks/from-as-casing/.

This fixes it, to remove a source of noise in logs (and because I agree with the suggestion that capitalizing keywords approves readability a bit).

[jameslamb]

The notebook builds should hopefully be fixed once rapidsai/cuspatial#1404 is merged

[jameslamb]

/ok to test

[jameslamb]

A couple of cuspatial notebooks are still failing. I've documented those in rapidsai/cuspatial#1406

[jameslamb]

Tests are passing here... looks like the fixes from #690 helped!

[jameslamb]

/merge

[jakirkham]

Thanks James and Kyle! 🙏