Fix EVP flagevaluation contract and enable Go system tests (#7180)

Author: leoromanovsky

manifests/golang.yml

@@ -886,7 +886,7 @@ manifest:
   tests/ffe/test_dynamic_evaluation.py::Test_FFE_RC_Unavailable: v2.4.0
   tests/ffe/test_dynamic_evaluation.py::Test_FFE_Unknown_Operator_Tolerance::test_unknown_operator_errors: bug (FFL-2182)
   tests/ffe/test_exposures.py: v2.6.0-dev  # Easy win for chi, echo, gin, net-http, net-http-orchestrion, uds-echo and version 2.5.0
-  tests/ffe/test_flag_eval_evp.py: missing_feature (FFL-2446)
+  tests/ffe/test_flag_eval_evp.py: v2.10.0-dev
   tests/ffe/test_flag_eval_metrics.py: v2.8.0
   tests/ffe/test_flag_eval_metrics.py::Test_FFE_Eval_Metric_Parse_Error_Invalid_Regex: irrelevant (Go validates regex at config load time)
   tests/ffe/test_flag_eval_metrics.py::Test_FFE_Eval_Nested_Attributes_Ignored: irrelevant (FFL-1980)

tests/ffe/test_flag_eval_evp.py

@@ -17,11 +17,11 @@
 
 RC_PRODUCT = "FFE_FLAGS"
 RC_PATH = f"datadog/2/{RC_PRODUCT}"
-EVP_FLAGEVALUATIONS_PATH = "/api/v2/flagevaluations"
+EVP_FLAGEVALUATIONS_PATH = "/api/v2/flagevaluation"
 EVP_WAIT_TIMEOUT_SECONDS = 30
 EVP_LOAD_WAIT_TIMEOUT_SECONDS = 60
 EVP_FULL_TIER_PER_FLAG_CAP = 10_000
-EVP_DEGRADATION_OVERFLOW_EVALS = 50
+EVP_DEGRADATION_OVERFLOW_EVALS = 2_000
 
 
 def make_multi_flag_fixture(flag_keys: list[str]) -> JSON: