Fixes non-interactive login flow and make sure "prompt" configuration is
respected by never prompting if it was explicitly disabled.
No longer asks to press Enter again after "Authentication complete"
message, since that didn't provide any value to the user.
This keeps git operations working even when PATH is modified, e.g. `brew
update` will work even though Homebrew runs the command explicitly
without `/usr/local/bin` in PATH.
Additionally, this inserts a blank value for `credential.*.helper` to
instruct git to ignore previously configured credential helpers, i.e.
those that might have been set up in system configuration files. We do
this because otherwise, git will store the credential obtained from gh
in every other credential helper in the chain, which we want to avoid.
Before:
git config --global credential.https://github.com.helper '!gh auth git-credential'
After:
git config --global credential.https://github.com.helper ''
git config --global --add credential.https://github.com.helper '!/path/to/gh auth git-credential'
