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/OpenApi/ProxySpec.hs

@@ -1,13 +1,14 @@
 module Feature.OpenApi.ProxySpec where
 
-import Network.Wai (Application)
-import Test.Hspec  hiding (pendingWith)
+import Test.Hspec hiding (pendingWith)
+
+import PostgREST.Config (AppConfig (..))
 
 import Protolude
 import SpecHelper
 
-spec :: SpecWith ((), Application)
-spec =
+spec :: SpecWithConfig
+spec withConfig = withConfig (baseCfg { configOpenApiServerProxyUri = Just "https://postgrest.com/openapi.json" }) $
   describe "GET / with proxy" $
     it "returns a valid openapi spec with proxy" $
       validateOpenApiResponse [("Accept", "application/openapi+json")]