krew fails to work if defaultRemoteName is assigned in ~/.gitconfig

[dustmop]

I have this config option set in my global ~/.gitconfig file:

[clone]
	defaultRemoteName = home

Which changes the default remote name to home. However, krew assumes that the default remote name is always going to be origin, due to

krew/internal/gitutil/git.go

Line 75 in efaaa22

return Exec(dir, "config", "--get", "remote.origin.url")

This causes most commands to fail:

> kubectl krew install [PACKAGE_NAME_HERE]
failed to retrieve plugin indexes: failed to list the remote URL for index default: command execution failure, output="": exit status 1

It would be better if one of the following were true:

1. krew would detect this setting and use the actual remote name
2. krew did not use this setting from the global config, perhaps by running with a blank config
3. The error message was better when GetRemoteURL returned empty data

[kundan2707]

/kind support