qemu: Add a secret object to/for a char source dev
    
    Add the secret object so the 'passwordid=' can be added if the command line
    if there's a secret defined in/on the host for TCP chardev TLS objects.
    
    Preparation for the secret involves adding the secinfo to the char source
    device prior to command line processing. There are multiple possibilities
    for TCP chardev source backend usage.
    
    Add test for at least a serial chardev as an example.