Alerting: Add method to provisioning API for obtaining a group and its rules (#51398) (#51761)

* Generate shell for new route

* Propagate path parameters

* Implement route logic

* Add a couple simple tests

* Use NotFound error for not found, avoid returning pointer

* Regenerate

(cherry picked from commit b9c7eb1380)

pkg/services/ngalert/api/tooling/api.json

@@ -355,7 +355,7 @@
    "type": "object",
    "x-go-package": "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
   },
-  "AlertRuleGroup": {
+  "AlertRuleGroupMetadata": {
    "properties": {
     "interval": {
      "format": "int64",
@@ -3373,6 +3373,7 @@
    "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
   },
   "alertGroup": {
+   "description": "AlertGroup alert group",
    "properties": {
     "alerts": {
      "description": "alerts",
@@ -3394,17 +3395,14 @@
     "labels",
     "receiver"
    ],
-   "type": "object",
-   "x-go-name": "AlertGroup",
-   "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
+   "type": "object"
   },
   "alertGroups": {
+   "description": "AlertGroups alert groups",
    "items": {
     "$ref": "#/definitions/alertGroup"
    },
-   "type": "array",
-   "x-go-name": "AlertGroups",
-   "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
+   "type": "array"
   },
   "alertStatus": {
    "description": "AlertStatus alert status",
@@ -3524,6 +3522,7 @@
    "$ref": "#/definitions/Duration"
   },
   "gettableAlert": {
+   "description": "GettableAlert gettable alert",
    "properties": {
     "annotations": {
      "$ref": "#/definitions/labelSet"
@@ -3582,20 +3581,16 @@
     "status",
     "updatedAt"
    ],
-   "type": "object",
-   "x-go-name": "GettableAlert",
-   "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
+   "type": "object"
   },
   "gettableAlerts": {
+   "description": "GettableAlerts gettable alerts",
    "items": {
     "$ref": "#/definitions/gettableAlert"
    },
-   "type": "array",
-   "x-go-name": "GettableAlerts",
-   "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
+   "type": "array"
   },
   "gettableSilence": {
-   "description": "GettableSilence gettable silence",
    "properties": {
     "comment": {
      "description": "comment",
@@ -3647,7 +3642,9 @@
     "status",
     "updatedAt"
    ],
-   "type": "object"
+   "type": "object",
+   "x-go-name": "GettableSilence",
+   "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
   },
   "gettableSilences": {
    "description": "GettableSilences gettable silences",
@@ -3783,6 +3780,7 @@
    "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
   },
   "postableSilence": {
+   "description": "PostableSilence postable silence",
    "properties": {
     "comment": {
      "description": "comment",
@@ -3822,11 +3820,10 @@
     "matchers",
     "startsAt"
    ],
-   "type": "object",
-   "x-go-name": "PostableSilence",
-   "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
+   "type": "object"
   },
   "receiver": {
+   "description": "Receiver receiver",
    "properties": {
     "name": {
      "description": "name",
@@ -3837,9 +3834,7 @@
    "required": [
     "name"
    ],
-   "type": "object",
-   "x-go-name": "Receiver",
-   "x-go-package": "github.com/prometheus/alertmanager/api/v2/models"
+   "type": "object"
   },
   "silence": {
    "description": "Silence silence",
@@ -4195,6 +4190,35 @@
    }
   },
   "/api/v1/provisioning/folder/{FolderUID}/rule-groups/{Group}": {
+   "get": {
+    "operationId": "RouteGetAlertRuleGroup",
+    "parameters": [
+     {
+      "in": "path",
+      "name": "FolderUID",
+      "required": true,
+      "type": "string"
+     },
+     {
+      "in": "path",
+      "name": "Group",
+      "required": true,
+      "type": "string"
+     }
+    ],
+    "responses": {
+     "200": {
+      "$ref": "#/responses/AlertRuleGroup"
+     },
+     "404": {
+      "description": " Not found."
+     }
+    },
+    "summary": "Get a rule group.",
+    "tags": [
+     "provisioning"
+    ]
+   },
    "put": {
     "consumes": [
      "application/json"
@@ -4217,15 +4241,15 @@
       "in": "body",
       "name": "Body",
       "schema": {
-       "$ref": "#/definitions/AlertRuleGroup"
+       "$ref": "#/definitions/AlertRuleGroupMetadata"
       }
      }
     ],
     "responses": {
      "200": {
-      "description": "AlertRuleGroup",
+      "description": "AlertRuleGroupMetadata",
       "schema": {
-       "$ref": "#/definitions/AlertRuleGroup"
+       "$ref": "#/definitions/AlertRuleGroupMetadata"
       }
      },
      "400": {