Add --depth option to support shallow cloning

[kevinb-khan]

Summary:

This is to support a faster dev setup process for designers and other non-engineers wishing to vibe code experiments in Khan/frontend.

Issue: None

Test plan:

• ka-clone --depth=1 git@github.com:Khan/webapp.git webapp2
• see that the webapp checkout is much faster

[zaquestion]

I had some discussion around this when I started here, but I don't think I ever followed up with any ka-clone changes. At the time @csilvers raised using --filter=blob:none to improve the clone speed, and it does reduce webapp by quite a bit, he seemed to believe it was superior to a shallow clone. If we're not already doing that, I'd suggest that we do that by default for webapp.

[zaquestion]

I'm good with this, I think we should still add a default for filterblob none. Presumably if this causes poor clones we can do some kind of repair. That said, I've got a feeling that Craig would prefer we didn't and that he has a clearer idea of the tradeoffs.

[kevinb-khan]

@zaquestion we won't be using --depth=1 by default anywhere. The design team will be testing things out using --depth=1 and if they run into issue we can remove it.

[csilvers]

@kevinb-khan it's possible that the filter is faster than --depth! In addition to not having the problems that shallow clones have. You might want to try it and replace the depth option with an option that uses the filter instead.