chore(cabal): update haskell language edition to GHC2021

This includes a good set of default language extensions that are
often used by us. It frees us of explicitly importing common extensions.

Ref: https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/control.html#extension-GHC2021

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>

test/observability/Observation/JwtCache.hs

@@ -1,6 +1,5 @@
-{-# LANGUAGE DataKinds        #-}
-{-# LANGUAGE NamedFieldPuns   #-}
-{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE DataKinds      #-}
+{-# LANGUAGE NamedFieldPuns #-}
 module Observation.JwtCache where
 
 import Network.Wai (Application)

test/observability/Observation/MetricsSpec.hs

@@ -1,8 +1,6 @@
 {-# LANGUAGE DataKinds           #-}
-{-# LANGUAGE FlexibleContexts    #-}
 {-# LANGUAGE MonadComprehensions #-}
 {-# LANGUAGE NamedFieldPuns      #-}
-{-# LANGUAGE TypeApplications    #-}
 
 module Observation.MetricsSpec where