Change compiler regression report to median (#7648)

This change the logic to find the baseline of the compiler regression.

before it find the max metric value from past 3-6 days as baseline
value, and compare it to the latest 3 days metric values.
however, this create some noisy alert. Change it to median value , to
avoid some scenarios such as shown below


<img width="393" height="201" alt="image"
src="https://github.com/user-attachments/assets/edeff7f8-09a8-494e-8127-b3b0984a297f"
/>

Author: yangw-dev

aws/lambda/benchmark_regression_summary_report/common/config.py

@@ -251,25 +251,25 @@
                 name="passrate",
                 condition="greater_equal",
                 threshold=0.9,
-                baseline_aggregation="max",
+                baseline_aggregation="median",
             ),
             "geomean_speedup": RegressionPolicy(
                 name="geomean_speedup",
                 condition="greater_equal",
                 threshold=0.95,
-                baseline_aggregation="max",
+                baseline_aggregation="median",
             ),
             "compression_ratio": RegressionPolicy(
                 name="compression_ratio",
                 condition="greater_equal",
                 threshold=0.95,
-                baseline_aggregation="max",
+                baseline_aggregation="median",
             ),
             "compilation_latency": RegressionPolicy(
                 name="compilation_latency",
                 condition="less_equal",
                 threshold=1.15,
-                baseline_aggregation="min",
+                baseline_aggregation="median",
             ),
         },
         notification_config={