Support the \additionalaffiliation command

[jozilla]

The acmart style has the ability to add a footnote for authors with multiple affiliations using the \additionalaffiliation{} command. It would be great to support this as an option for the author block. In LaTeX, it works as follows:

\author{John Doe}
\additionalaffiliation{%
  \institution{Stanford University}
  \city{Stanford}
  \state{CA}
  \country{USA}
}
\affiliation{%
  \institution{Acme, Inc.}
  \city{Chicago} 
  \state{IL} 
  \country{USA}
}
\email{john@stanford.edu}

This could be supported in the following way (here, with all authors sharing an affiliation, but the first having an additional affiliation).

author:
  - name: John Doe
    email: john@stanford.edu
    additionalaffiliation:
     name: Stanford University
     city: Stanford
     state: CA
     country: USA
  - name: Jeff Wayne
    email: jeff@acme.com
  - name: Emily Riker
    email: emily@acme.com
    affiliation:
      name: Acme, Inc.
      city: Chicago
      state: IL
      country: USA

Right now, this doesn't result in an error but also doesn't produce the desired result (there's no footnote added).