JATS: proper way to add license/copyright info

[castedo]

Currently LaTeXML outputs

      <permissions>
        <copyright-statement>unknown</copyright-statement>
      </permissions>

whereas pandoc outputs (when given metadata in YAML):

      <permissions>
        <copyright-statement>Copyright © 2020 S. Maggi</copyright-statement>
        <copyright-year>2020</copyright-year>
        <copyright-holder>S. Maggi</copyright-holder>
        <license license-type="open-access">
          <ali:license_ref xmlns:ali="http://www.niso.org/schemas/ali/1.0/">https://creativecommons.org/licenses/by/4.0/</ali:license_ref>
          <license-p>Released under a Creative Commons Attribution 4.0 International license.</license-p>
        </license>
      </permissions>

which seems to be proper according to JATS4R.

Kind of related to #2351 in that maybe this kind of data should not be in LaTeX source code and instead injected into JATS XML via a very different mechanism that what LaTeXML usually does.