move search header into document split

[dnoneill]

update default number of result to 20. Closes #1171

Quick notes

• app/views/catalog/_document_split.html.erb is overriding and override from geoblacklight. The only real change is to add in <%= render blacklight_config.view_config(document_index_view_type).search_header_component.new %> above turbo-frame
• app/views/catalog/_search_header.html.erb is an override from blacklight. In blacklight it renders the search_header_component which has a partial with <%= render 'did_you_mean' %> <%= render 'sort_and_per_page' %> so I just moved everything into this file and removed sort_and_per_page which is a partial where the only thing in it is render blacklight_config.view_config(document_index_view_type).search_header_component.new