Short name for "--group" option

[hongquan]

Summary

Add short name -G for --group option in uv add command.

The uv add --group command is used quite often. Having short alternative form uv add -G will let user type less.
The -G short name also exists in Poetry and PDM.

Test Plan

$ uv help add

...

Options:
  -G, --group <GROUP>
          Add the requirements to the specified dependency group.

[zanieb]

I'm a little hesitant to use an uppercase short flag, I'm not sure we're really doing that elsewhere. Why do they use -G instead of -g? What's pip going to do for the short flag?

[hongquan]

PDM uses -G instead of -g because it already has -g / --global.

[hongquan]

@zanieb should I change it to lowercase?