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/ExtraSearchPathSpec.hs

@@ -1,16 +1,17 @@
 module Feature.ExtraSearchPathSpec where
 
 import Network.HTTP.Types
-import Network.Wai         (Application)
 import Test.Hspec
 import Test.Hspec.Wai
 import Test.Hspec.Wai.JSON
 
+import PostgREST.Config (AppConfig (..))
+
 import Protolude  hiding (get)
 import SpecHelper
 
-spec :: SpecWith ((), Application)
-spec = describe "extra search path" $ do
+spec :: SpecWithConfig
+spec withConfig = withConfig (baseCfg { configDbExtraSearchPath = ["public", "extensions", "EXTRA \"@/\\#~_-"] }) $ describe "extra search path" $ do
 
   it "finds the ltree <@ operator on the public schema" $
     request methodGet "/ltree_sample?path=cd.Top.Science.Astronomy" [] ""