Locations: Rename "Jisc KB" to "Jisc NBK"

[tosteiner]

Currently, Jisc KB is being listed as one of the Locations of a given book. As has been established, Jisc KB has ceased operations, with Jisc NBK - the National Bibliographic Knowledgebase - will be the Jisc database that we will be submitting books to.

Hence, it'd be good to update the "Jisc KB" entry in the list of locations to "Jisc NBK"

[rhigman]

Do we know whether those locations still work? Will the URLs ultimately redirect to Jisc NBK pages, or somewhere else, or nowhere at all? Will a legacy KB be maintained that's separate from NBK? We should be clear on all this before updating the entry. It might be that the existing Jisc KB links are now all defunct (should they therefore be removed?), or it might be that they continue to exist on a legacy platform that's distinct from Jisc NBK, in which case we'd need to maintain both Jisc KB and Jisc NBK as separate location platform options.

(Similarly, we list "Jisc KB" as one of the platforms which accepts Thoth metadata exports. We would need to find out whether Jisc NBK would still accept the same output format(s) before updating that.)