chore: change server timing render to response

"render" is a loaded term than might be thought as the generation
of a full HTML page. While for this phase we only process the status
and the headers.

Changing it to "response" so is not misleading at least. Users can check the
docs for clarification.

src/PostgREST/Response/Performance.hs

@@ -13,7 +13,7 @@ import           Protolude
 data ServerMetric =
     SMJwt
   | SMParse
-  | SMRender
+  | SMResp
   | SMPlan
   | SMTransaction
   deriving (Show, Eq, Ord)
@@ -21,7 +21,7 @@ type ServerTimingData = Map ServerMetric (Maybe Double)
 
 -- | Render the Server-Timing header from a ServerTimingData
 --
--- >>> renderServerTimingHeader $ Map.fromList [(SMPlan, 0.1), (SMTransaction, 0.2), (SMRender, 0.3), (SMJwt, 0.4)]
+-- >>> renderServerTimingHeader $ Map.fromList [(SMPlan, 0.1), (SMTransaction, 0.2), (SMResp, 0.3), (SMJwt, 0.4)]
 -- ("Server-Timing","jwt;dur=400000.0, render;dur=300000.0, plan;dur=100000.0, query;dur=200000.0")
 renderServerTimingHeader :: ServerTimingData -> HTTP.Header
 renderServerTimingHeader timingData =
@@ -31,6 +31,6 @@ renderTiming (metric, time) = maybe "" (\x -> BS.concat [renderMetric metric, BS
   where
     renderMetric SMPlan        = "plan"
     renderMetric SMTransaction = "transaction"
-    renderMetric SMRender      = "render"
+    renderMetric SMResp        = "response"
     renderMetric SMJwt         = "jwt"
     renderMetric SMParse       = "parse"