Add odcs-credential-helper executable
    
    This script reads raw config source name from the environment variable,
    and receives repo URL from git. That is sufficient information to look
    up corresponding credentials (if any) and return them to git.
    
    The helper refuses to work if the suggested protocol is not https. This
    is to prevent the credentials from being sent over unencrypted channel.
    
    JIRA: RHELCMP-11808