Support for Gallica API from the BNF

[dietervu]

See https://api.bnf.fr/fr/api-document-de-gallica#scroll-nav__10 for details.

This API can provide an HTML view of a textual resource for a specific ARK identifier

e.g. https://gallica.bnf.fr/ark:/12148/bpt6k5619759j then can be accessed via
https://gallica.bnf.fr/ark:/12148/bpt6k5619759j.texteBrut

which then in turn can be provided to the Switchboard (which then will need to use the extract text option to convert the HTML into plain text)