Fixes the missing sort call in add_sorting_to_solr (#5905).

[bwatson78]

Fixes #5905 ; refs #5905

Because our override method never calls Blacklight::SearchBuilder#sort, it will always default to title_si asc, making the sort options useless on this show page.

Changes proposed in this pull request:

• Adds the missing sort command to the method that overrides one from Blacklight::Solr::SearchBuilderBehavior.
• Inserts a test to confirm that a sort option passed into the blacklight_params actually gets utilized.

Guidance for testing, such as acceptance criteria or new user interface behaviors:

• Login and visit Dashboard
• Choose Collections and select one with multiple works to navigate to the show page
• Choose any sort option from the pull down menu
• After page load, the order of the works should be different

@samvera/hyrax-code-reviewers

[cjcolvar]

Nice catch!