Alerting: Receivers API (read only endpoints) (#81751)

* Add single receiver method

* Add receiver permissions

* Add single/multi GET endpoints for receivers

* Remove stable tag from time intervals

See end of PR description here: https://github.com/grafana/grafana/pull/81672

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

@@ -4512,7 +4512,6 @@
    "type": "object"
   },
   "alertGroup": {
-   "description": "AlertGroup alert group",
    "properties": {
     "alerts": {
      "description": "alerts",
@@ -4536,6 +4535,7 @@
    "type": "object"
   },
   "alertGroups": {
+   "description": "AlertGroups alert groups",
    "items": {
     "$ref": "#/definitions/alertGroup"
    },
@@ -4640,6 +4640,7 @@
    "type": "object"
   },
   "gettableAlert": {
+   "description": "GettableAlert gettable alert",
    "properties": {
     "annotations": {
      "$ref": "#/definitions/labelSet"
@@ -4701,7 +4702,6 @@
    "type": "array"
   },
   "gettableSilence": {
-   "description": "GettableSilence gettable silence",
    "properties": {
     "comment": {
      "description": "comment",
@@ -4756,6 +4756,7 @@
    "type": "array"
   },
   "integration": {
+   "description": "Integration integration",
    "properties": {
     "lastNotifyAttempt": {
      "description": "A timestamp indicating the last attempt to deliver a notification regardless of the outcome.\nFormat: date-time",
@@ -4936,7 +4937,6 @@
    "type": "object"
   },
   "receiver": {
-   "description": "Receiver receiver",
    "properties": {
     "active": {
      "description": "active",
@@ -7046,6 +7046,86 @@
     ]
    }
   },
+  "/v1/notifications/receivers": {
+   "get": {
+    "operationId": "RouteGetReceivers",
+    "parameters": [
+     {
+      "in": "query",
+      "items": {
+       "type": "string"
+      },
+      "name": "names",
+      "type": "array"
+     },
+     {
+      "format": "int64",
+      "in": "query",
+      "name": "limit",
+      "type": "integer"
+     },
+     {
+      "format": "int64",
+      "in": "query",
+      "name": "offset",
+      "type": "integer"
+     },
+     {
+      "in": "query",
+      "name": "decrypt",
+      "type": "boolean"
+     }
+    ],
+    "responses": {
+     "200": {
+      "$ref": "#/responses/GetReceiversResponse"
+     },
+     "403": {
+      "description": "PermissionDenied",
+      "schema": {
+       "$ref": "#/definitions/PermissionDenied"
+      }
+     }
+    },
+    "summary": "Get all receivers.",
+    "tags": [
+     "notifications"
+    ]
+   }
+  },
+  "/v1/notifications/receivers/{Name}": {
+   "get": {
+    "operationId": "RouteGetReceiver",
+    "parameters": [
+     {
+      "in": "path",
+      "name": "name",
+      "required": true,
+      "type": "string"
+     },
+     {
+      "in": "query",
+      "name": "decrypt",
+      "type": "boolean"
+     }
+    ],
+    "responses": {
+     "200": {
+      "$ref": "#/responses/GetReceiverResponse"
+     },
+     "404": {
+      "description": "NotFound",
+      "schema": {
+       "$ref": "#/definitions/NotFound"
+      }
+     }
+    },
+    "summary": "Get a receiver by name.",
+    "tags": [
+     "notifications"
+    ]
+   }
+  },
   "/v1/notifications/time-intervals": {
    "get": {
     "description": "Get all the time intervals",
@@ -8507,6 +8587,21 @@
     "$ref": "#/definitions/GettableTimeIntervals"
    }
   },
+  "GetReceiverResponse": {
+   "description": "",
+   "schema": {
+    "$ref": "#/definitions/GettableApiReceiver"
+   }
+  },
+  "GetReceiversResponse": {
+   "description": "",
+   "schema": {
+    "items": {
+     "$ref": "#/definitions/GettableApiReceiver"
+    },
+    "type": "array"
+   }
+  },
   "GettableHistoricUserConfigs": {
    "description": "",
    "schema": {