Add a link to "Translate this page" to every Docs Hub page

[amandastevens]

There are links at the top of every page on the Docs Hub to "Edit this page" and "Make a suggestion." A user suggested we add a link to "Translate this page" which links to Crowdin (PKP's documentation tool) and opens the corresponding page where a user can make a translation (or something similar, to the extent that this is technically possible). This could lead to more translations being made of PKP documentation.