add: config db-timezone-enabled for optional querying of timezones

To avoid repeated querying of `pg_timezone_names` every time schema
cache is reset, `Prefer: timezone` can be disabled by setting
`db-timezone-enabled = false`.

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

test/spec/SpecHelper.hs

@@ -132,6 +132,7 @@ baseCfg = let secret = encodeUtf8 "reallyreallyreallyreallyverysafe" in
   , configDbSchemas                 = fromList ["test"]
   , configDbConfig                  = False
   , configDbPreConfig               = Nothing
+  , configDbTimezoneEnabled         = True
   , configDbUri                     = "postgresql://"
   , configFilePath                  = Nothing
   , configJWKS                      = rightToMaybe $ parseSecret secret
@@ -254,6 +255,9 @@ testCfgServerTiming = baseCfg { configDbPlanEnabled = True }
 testCfgAggregatesEnabled :: AppConfig
 testCfgAggregatesEnabled = baseCfg { configDbAggregates = True }
 
+testCfgTimezoneDisabled :: AppConfig
+testCfgTimezoneDisabled = baseCfg { configDbTimezoneEnabled = False }
+
 analyzeTable :: Text -> IO ()
 analyzeTable tableName =
   void $ readProcess "psql" ["-U", "postgres", "--set", "ON_ERROR_STOP=1", "-a", "-c", toS $ "ANALYZE test.\"" <> tableName <> "\""] []