Add RPC API check

ci/localnet-sanity.sh

@@ -82,6 +82,15 @@ echo "--- Node count"
   rm -rf $client_id
 ) || flag_error
 
+echo "--- RPC API: getTransactionCount"
+(
+  set -x
+  curl -X POST \
+    -H 'Content-Type: application/json' \
+    -d '{"jsonrpc":"2.0","id":1, "method":"getTransactionCount"}' \
+    http://localhost:8899
+) || flag_error
+
 killBackgroundCommands
 
 echo "--- Ledger verification"