AlertingNG: base API implementation (#31824)

* AlertingNG: base API implementation

* Pass the interface instead of the base impl

* Ruler mock draft (WIP)

* Update alerting-api dependency

* Improve mock implementation

pkg/services/ngalert/api/test-data/post-rulegroup-data.json

@@ -0,0 +1,30 @@
+{
+  "name": "group42",
+  "interval": "10s",
+  "rules": [
+    {
+      "expr": "",
+      "grafana_alert": {
+        "title": "something completely different",
+        "condition": "A",
+        "data": [
+          {
+            "refId": "A",
+            "queryType": "",
+            "relativeTimeRange": {
+              "from": 18000,
+              "to": 10800
+            },
+            "model": {
+              "datasource": "__expr__",
+              "type": "math",
+              "expression": "2 + 2 > 1"
+            }
+          }
+        ],
+        "no_data_state": "NoData",
+        "exec_err_state": "Alerting"
+      }
+    }
+  ]
+}