Add preview citation to OBIS EML and ERDDAP snippet

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The citation preview that is generated on the contact page can be included in some outputted XML:

In the EML, it can appear under <citation> below. This way it can be populated in the OBIS IPT:

  <additionalMetadata>
    <metadata>
      <gbif>
          <dateStamp>2020-02-12T09:19:51.053+01:00</dateStamp>
          <hierarchyLevel>dataset</hierarchyLevel>
            <citation identifier="http://dx.doi.org/10.21966/1.566666">Johnson B, Hunt B (2020): Hakai Institute Juvenile Salmon Program. v1.25. Canadian node of the Ocean Biogeographic Information System (OBIS Canada). Dataset/Samplingevent. http://dx.doi.org/10.21966/1.566666</citation>
            <formationPeriod>2015-05-01</formationPeriod>
          <dc:replaces>72de3af4-1572-4f2d-8006-2bfa2007065c/v1.25.xml</dc:replaces>
      </gbif>
    </metadata>
  </additionalMetadata>
</eml:eml>

In the ERDDAP snippet, it can appear under reference in the dataset globals

<att name="references">Johnson B, Hunt B (2020): Hakai Institute Juvenile Salmon Program. v1.25. Canadian node of the Ocean Biogeographic Information System (OBIS Canada). Dataset/Samplingevent. http://dx.doi.org/10.21966/1.566666</att>

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Not sure where to put the citation text in erddap - we are currently setting references to DOI, which is a better fit - https://wiki.esipfed.org/Attribute_Convention_for_Data_Discovery_1-3#references

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The OBIS part is done

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relevant discussion on the ERDDAP mailing list this week https://groups.google.com/g/erddap/c/k58VhLE7MhA/m/QKl4-101AAAJ?utm_medium=email&utm_source=footer&pli=1