Flag to specify particular version

[JoshOrndorff]

Since the scripts always download the latest available version of substrate (or the ui etc) it is challenging to use these scripts when following published tutorials. This situation has led to eg https://github.com/shawntabrizi/substrate-package being created and maintained.

I would like to specify something like --source <commit hash> to get a particular version.

[ltfschoen]

here's a similar example for reference, just need to tweak it https://github.com/paritytech/scripts/pull/56/files#diff-b7b79349393e65ecfcc7c4cd6c9e8e11R225