Rename to performance

This is consistent with the old performance platform URLs, which were
gov.uk/performance, and others that we have like /pricing and /features

app/main/views/performance.py

@@ -0,0 +1,17 @@
+from datetime import datetime, timedelta
+
+from flask import jsonify
+
+from app import performance_dashboard_api_client
+from app.main import main
+
+
+@main.route("/performance")
+def performance():
+    api_args = {}
+
+    api_args['start_date'] = (datetime.utcnow() - timedelta(days=90)).date()
+    api_args['end_date'] = datetime.utcnow().date()
+
+    stats = performance_dashboard_api_client.get_performance_dashboard_stats(api_args)
+    return jsonify(stats)