Allow indexingHint property in info.yml to generate json-ld block for SEO

[edsilv]

IIIF/api#438

e.g. indexingHint: "schema:author"

https://www.adamvowles.co.uk/blog/json-ld-local/

Should this be a separate lib to biiif? Perhaps presentation api and json-ld are plugins?

[edsilv]

include link to json-ld block via seeAlso as per:

https://wellcomelibrary.org/iiif/b18035978/manifest
https://wellcomelibrary.org/resource/schemaorg/b18035978

Include in page as per:
view-source:https://wellcomelibrary.org/item/b18035978

[edsilv]

example: https://gist.github.com/edsilv/8e0e6da9342585b824908efc40bd69d2

via: https://scrc.lib.ncsu.edu/sal_staging/catalog/ua023_015-005-bx0002-014-019#?c=0&m=0&s=0&cv=0&z=-648.8887%2C0%2C2097.7774%2C1189