Relative URIs for Resource URLs in SOLR

[JVickery-TBS]

This is a solution to the Resource URLs in open-data/ckanext-language-domains#1

Basically the absolute URI of a resource is not stored in the database, but the res_url is stored in SOLR with a fully qualified URI for upload types. Instead, we modify code here to not store qualified URIs in SOLR and just add the requesting hostname to upload resource types for their download URI. And just add a for_index context when indexing packages/resources so that SOLR will always have the relative paths.

I imagine this would kind of break other frameworkable parts of CKAN resource uploader...maybe. So not fitting for upstream contrib.

[JVickery-TBS]

Oh also just a note about for_index context - I did this instead of using for_view or a new for_api because I was unable to handle it that way in ckanapi LocalCKAN

[wardi]

I think it's reasonable to have something like this in core: always store uploaded files with relative paths. I'd be a little happier if it didn't rely on a context variable sent to package_show.

Note that this will break when we upgrade because the SynchronousSearchPlugin goes away.