Add filter for free digital material

[lrosenstrom]

See description in LWS-242.

• Add optional filter for free e-resources for lxl-web/Libris sök. The filter can be formulated in the lxl web query language like so (which is sort of a hack, but will do until the free nature of things is expressed more clearly in the data):

(usageAndAccessPolicy.label:"gratis" OR "associatedMedia.marc:publicNote":"*fritt tillgänglig*") AND hasInstanceType:"Electronic"

• Add MediaObject-cards definition to include marc:publicNote in the search index, and hence facilitate the query above.

Edit: @olovy pointed out that we should probably add https://id.kb.se/policy/freely-available and https://id.kb.se/policy/oa/gratis to the filter, so those two access policies are also included now.

[olovy]

Note that we can't be sure that e.g. usageAndAccessPolicy and type:Electronic match the same instance since instances are not nested in ES. This should not be a problem in practice. And as you say, the filter should be based on more exact symbols.

See comment about wildcards. Other than that, LGTM

[olovy]

LGTM!

[kwahlin]

LGTM