test(spec): inline config into test suite

Previously, information about each test-suite was repeated in 3 separate
places:
- as a label and as implicit knowledge in the test-suite itself,
- as a comment in Main.hs, and
- as a configuration in SpecHelper.hs.

With this change, there will be a single source of truth in the test
suite itself. This will allow a single test-suite to easily test
multiple different configurations.

test/spec/Feature/Query/ErrorSpec.hs

@@ -1,7 +1,5 @@
 module Feature.Query.ErrorSpec where
 
-import Network.Wai (Application)
-
 import Network.HTTP.Types
 import Test.Hspec
 import Test.Hspec.Wai
@@ -10,8 +8,8 @@ import Test.Hspec.Wai.JSON
 import Protolude  hiding (get)
 import SpecHelper
 
-pgErrorCodeMapping :: SpecWith ((), Application)
-pgErrorCodeMapping = do
+pgErrorCodeMapping :: SpecWithConfig
+pgErrorCodeMapping withConfig = withConfig baseCfg $ do
   describe "PostreSQL error code mappings" $ do
     it "should return 500 for cardinality_violation" $
       get "/bad_subquery" `shouldRespondWith` 500