devenv: disable managed-alerts for datasources (#42295)

devenv/datasources.yaml

@@ -34,11 +34,15 @@ datasources:
     type: prometheus
     access: proxy
     url: http://localhost:9090
+    jsonData:
+      manageAlerts: false
 
   - name: gdev-slow-prometheus
     type: prometheus
     access: proxy
     url: http://localhost:3011
+    jsonData:
+      manageAlerts: false
 
   - name: gdev-testdata
     isDefault: true
@@ -293,6 +297,7 @@ datasources:
     url: http://localhost:3100
     editable: false
     jsonData:
+      manageAlerts: false
       derivedFields:
         - name: "traceID"
           matcherRegex: "traceID=(\\w+)"