stop storing raw data in the solr index

[hancush]

via @evz's fancy training!

we default to storing the raw value for all fields indexed by solr. this is useful if you want to display results without round-tripping to the database. haystack does this round-tripping for us, so the raw data isn't doing us any favors. in fact, it means that all this raw data is taking up a bunch of memory and space, for no reason. let's update our solr configs to not store the raw data.

example from la metro schema.xml:

    <field name="sponsorships_exact" type="string" indexed="true" stored="true" multiValued="true" />

    <field name="inferred_status_exact" type="string" indexed="true" stored="true" multiValued="false" />

    <field name="attachment_text" type="text_en" indexed="true" stored="true" multiValued="false" />

    <field name="source_url" type="string" indexed="false" stored="true" multiValued="false" />

    <field name="identifier" type="text_en" indexed="true" stored="true" multiValued="false" />

[hancush]

Relevant documentation in Haystack.