ref(performance): add referrer for performance change explorer (#54211)

Adds the reference for the performance change explorer referrer for the
profileFunctions api call.

src/sentry/snuba/referrer.py

@@ -325,6 +325,7 @@ class Referrer(Enum):
     API_PROFILING_LANDING_CHART = "api.profiling.landing-chart"
     API_PROFILING_LANDING_TABLE = "api.profiling.landing-table"
     API_PROFILING_LANDING_FUNCTIONS_CARD = "api.profiling.landing-functions-card"
+    API_PROFILING_PERFORMANCE_CHANGE_EXPLORER = "api.profiling.performance-change-explorer"
     API_PROFILING_PROFILE_SUMMARY_CHART = "api.profiling.profile-summary-chart"
     API_PROFILING_PROFILE_SUMMARY_TOTALS = "api.profiling.profile-summary-totals"
     API_PROFILING_PROFILE_SUMMARY_TABLE = "api.profiling.profile-summary-table"