fix: Dump media handlers and timezones with --dump-schema

Those were left out of the schema dump when the features were introduced, probably
because ByteString doesn't have a toJSON instance. Changing the type to Text solves
this easily.

Resolves #3237

src/PostgREST/ApiRequest/Preferences.hs

@@ -163,7 +163,7 @@ fromHeaders allowTxDbOverride acceptedTzNames headers =
     listStripPrefix prefix prefList = listToMaybe $ mapMaybe (BS.stripPrefix prefix) prefList
 
     timezonePref = listStripPrefix "timezone=" prefs
-    isTimezonePrefAccepted = (S.member <$> timezonePref <*> pure acceptedTzNames) == Just True
+    isTimezonePrefAccepted = (S.member <$> (decodeUtf8 <$> timezonePref) <*> pure acceptedTzNames) == Just True
 
     maxAffectedPref = listStripPrefix "max-affected=" prefs >>= readMaybe . BS.unpack