Docs: Add example for updating dashboard panel alert rule (#25260)

docs/sources/http_api/dashboard.md

@@ -60,6 +60,163 @@ JSON Body schema:
 - **overwrite** – Set to true if you want to overwrite existing dashboard with newer version, same dashboard title in folder or same dashboard uid.
 - **message** - Set a commit message for the version history.
 
+For adding or updating an alert rule for a dashboard panel the user should declare a
+`dashboard.panels.alert` block.
+
+**Example Request for updating dashboard alert rule**:
+
+```http
+HTTP/1.1 200 OK
+Content-Type: application/json; charset=UTF-8
+Content-Length: 78
+
+{
+ "dashboard":  {
+        "id": 104,
+        "panels": [
+            {
+                "alert": {
+                    "alertRuleTags": {},
+                    "conditions": [
+                        {
+                            "evaluator": {
+                                "params": [
+                                    25
+                                ],
+                                "type": "gt"
+                            },
+                            "operator": {
+                                "type": "and"
+                            },
+                            "query": {
+                                "params": [
+                                    "A",
+                                    "5m",
+                                    "now"
+                                ]
+                            },
+                            "reducer": {
+                                "params": [],
+                                "type": "avg"
+                            },
+                            "type": "query"
+                        }
+                    ],
+                    "executionErrorState": "alerting",
+                    "for": "5m",
+                    "frequency": "1m",
+                    "handler": 1,
+                    "name": "Panel Title alert",
+                    "noDataState": "no_data",
+                    "notifications": []
+                },
+                "aliasColors": {},
+                "bars": false,
+                "dashLength": 10,
+                "dashes": false,
+                "datasource": null,
+                "fieldConfig": {
+                    "defaults": {
+                        "custom": {}
+                    },
+                    "overrides": []
+                },
+                "fill": 1,
+                "fillGradient": 0,
+                "gridPos": {
+                    "h": 9,
+                    "w": 12,
+                    "x": 0,
+                    "y": 0
+                },
+                "hiddenSeries": false,
+                "id": 2,
+                "legend": {
+                    "avg": false,
+                    "current": false,
+                    "max": false,
+                    "min": false,
+                    "show": true,
+                    "total": false,
+                    "values": false
+                },
+                "lines": true,
+                "linewidth": 1,
+                "nullPointMode": "null",
+                "options": {
+                    "dataLinks": []
+                },
+                "percentage": false,
+                "pointradius": 2,
+                "points": false,
+                "renderer": "flot",
+                "seriesOverrides": [],
+                "spaceLength": 10,
+                "stack": false,
+                "steppedLine": false,
+                "targets": [
+                    {
+                        "refId": "A",
+                        "scenarioId": "random_walk"
+                    }
+                ],
+                "thresholds": [
+                    {
+                        "colorMode": "critical",
+                        "fill": true,
+                        "line": true,
+                        "op": "gt",
+                        "value": 50
+                    }
+                ],
+                "timeFrom": null,
+                "timeRegions": [],
+                "timeShift": null,
+                "title": "Panel Title",
+                "tooltip": {
+                    "shared": true,
+                    "sort": 0,
+                    "value_type": "individual"
+                },
+                "type": "graph",
+                "xaxis": {
+                    "buckets": null,
+                    "mode": "time",
+                    "name": null,
+                    "show": true,
+                    "values": []
+                },
+                "yaxes": [
+                    {
+                        "format": "short",
+                        "label": null,
+                        "logBase": 1,
+                        "max": null,
+                        "min": null,
+                        "show": true
+                    },
+                    {
+                        "format": "short",
+                        "label": null,
+                        "logBase": 1,
+                        "max": null,
+                        "min": null,
+                        "show": true
+                    }
+                ],
+                "yaxis": {
+                    "align": false,
+                    "alignLevel": null
+                }
+            }
+        ],
+        "title": "Update alert rule via API",
+        "uid": "dHEquNzGz",
+        "version": 1
+    }
+}
+```
+
 **Example Response**:
 
 ```http