chore(ci): add product cost for rtx4090 to compute throughput

RTX4090 we're using here is owned by Zama. So we don't pay an
hourly rate to AWS per se. But in ordrer to compute throughput on
benchmarks results, the parser needs a numeric value corresponding
to the hardware used. Ops-per-dollar metric is not really used
today conversely ops-per-seconds is.
In the end we use an approximation of the cost for electrical
consumption.

ci/ec2_products_cost.json

@@ -3,5 +3,6 @@
   "hpc7a.96xlarge": 7.7252,
   "p3.2xlarge": 3.06,
   "p4d.24xlarge": 32.7726,
-  "p5.48xlarge": 98.32
+  "p5.48xlarge": 98.32,
+  "rtx4090": 0.04
 }