feat: Add option to turn off setup of shell completion

[mmcrockett]

Issue

• When I moved from Linux => Mac I didn't have bash completion package installed and so got these errors (plus turns out I really prefer to complete on filenames even though the branch complete is a nice feature)

Screenshot of errors I see:

Proposed Fix

• Add an option git_skip_shell_completion that is backward compatible and will ignore any shell completion setup

[mmcrockett]

I had considered moving all shell completion to one spot but couldn't decide if that was better/worse than having the completion near the function (ie complete for branch is in lib/git/branch_shortcuts.sh. If that would help the code organization, let me know and I can do a follow-up PR.

[ghthor]

I had considered moving all shell completion to one spot but couldn't decide if that was better/worse than having the completion near the function (ie complete for branch is in lib/git/branch_shortcuts.sh. If that would help the code organization, let me know and I can do a follow-up PR.

I like this idea, 👍 from me