Include `extra` images in Sample Image Size Report

[lbussell]

The extra image variant is not included in the Sample Image Size Report. The report should be updated to include the extra image variant so users can understand how adding ICU/tzdata/etc. libraries affects image size.

[lbussell]

@richlander I'm going to have to deprioritize this to focus on dotnet/docker-tools#1264. You or @MichaelSimons are welcome to pick it up if you have time.

[lbussell]

Moving this to RC1 timeframe.

As part of this work I'd also like to make the results in the table more easily reproducible.