Allow manually calling search-api-v2

As a first step to building the integration with `search-api-v2`, allow
`finder-frontend` to call it if and only if an explicit `use_v2` query
parameter is supplied.

- Bump `gds-api-adapters` to get new adapter for `search-api-v2`
- Add `Services#search_api_v2`
- Update `Search::Query` to call `search-api-v2` if `use_v2` parameter
  is present and truthy (accoring to `ActiveModel::Type::Boolean`)

app/lib/search/query.rb

@@ -87,7 +87,11 @@ def fetch_search_response(content_item)
         override_sort_for_feed:,
       ).call
 
-      if queries.one?
+      if use_v2_api?
+        GovukStatsd.time("search_api_v2.finder_search") do
+          Services.search_api_v2.search(queries.first).to_hash
+        end
+      elsif queries.one?
         GovukStatsd.time("rummager.finder_search") do
           Services.rummager.search(queries.first).to_hash
         end
@@ -99,5 +103,9 @@ def fetch_search_response(content_item)
         end
       end
     end
+
+    def use_v2_api?
+      ActiveModel::Type::Boolean.new.cast(filter_params["use_v2"])
+    end
   end
 end

app/lib/services.rb

@@ -25,6 +25,10 @@ def self.rummager
     GdsApi::Search.new(Plek.find("search-api"))
   end
 
+  def self.search_api_v2
+    GdsApi::SearchApiV2.new(Plek.find("search-api-v2"))
+  end
+
   def self.email_alert_api
     Services::EmailAlertApi.new
   end

spec/lib/search/query_spec.rb

@@ -5,6 +5,10 @@ def stub_search
     stub_request(:get, %r{#{Plek.find("search-api")}/search.json})
   end
 
+  def stub_search_v2
+    stub_request(:get, %r{#{Plek.find("search-api-v2")}/search.json})
+  end
+
   def stub_batch_search
     stub_request(:get, %r{#{Plek.find("search-api")}/batch_search.json})
   end
@@ -45,6 +49,24 @@ def result_item(id, title, score:, popularity:, updated:)
     }
   end
 
+  context "when manually overriding parameters to use the v2 API" do
+    subject { described_class.new(content_item, { "use_v2" => "true" }).search_results }
+
+    before do
+      stub_search_v2.to_return(body: {
+        "results" => [
+          result_item("/i-am-the-v2-api", "I am the v2 API", score: nil, updated: "14-12-19", popularity: 1),
+        ],
+      }.to_json)
+    end
+
+    it "calls the v2 API" do
+      results = subject.fetch("results")
+      expect(results.length).to eq(1)
+      expect(results.first).to match(hash_including("_id" => "/i-am-the-v2-api"))
+    end
+  end
+
   context "when searching using a single query" do
     subject { described_class.new(content_item, filter_params).search_results }