Install DynamicPageList extension on the public wiki

https://www.mediawiki.org/wiki/Extension:DynamicPageList_(Wikimedia)

This will allow us to embed the list of internships on directly on this page: https://wiki.softwareheritage.org/wiki/Google_Summer_of_Code_2020#Research_internships

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Migrated from T2253 (view on Phabricator)