node: increase batch limits for auth rpc API (#27924)

This raises the JSON-RPC batch request limits significantly for the engine API endpoint.
The limits are now also hard-coded, so users won't get them wrong. I have chosen these limits:

    maximum batch items: 2000
    maximum batch response size: 250MB

While it would also be possible to disable batch limits completely for the engine API, 
I think having some limits is a good safety net against misbehaving CLs. Since this
 isn't configurable, we really want to ensure this limit will never become an issue in the
 CL/EL communication, so I set them quite high.

---------

Signed-off-by: jsvisa <delweng@gmail.com>
Co-authored-by: Felix Lange <fjl@twurst.com>

node/defaults.go

@@ -36,6 +36,13 @@ const (
 	DefaultAuthPort = 8551        // Default port for the authenticated apis
 )
 
+const (
+	// Engine API batch limits: these are not configurable by users, and should cover the
+	// needs of all CLs.
+	engineAPIBatchItemLimit         = 2000
+	engineAPIBatchResponseSizeLimit = 250 * 1000 * 1000
+)
+
 var (
 	DefaultAuthCors    = []string{"localhost"} // Default cors domain for the authenticated apis
 	DefaultAuthVhosts  = []string{"localhost"} // Default virtual hosts for the authenticated apis