add git-prompt module

[amtoine]

should

• close should we include git related prompts? #9

description

this prompt comes from amtoine/scripts in the nu-scripts package, module shell_prompt.

it can be used as

use nu-git-manager-sugar git-prompt setup
setup --duration-threshold 10sec --indicators {
    vi: {
        insert: "> "
        normal: "> "
    }
}

Important
i did not add tests for this right now, only TODOs on all the commands i believe should be tested 😉