Docs: update annotations API docs to include required field (#52644)

* Update annotations.md

A minor change to include the required fields when creating a new annotation via the annotations API. The error message when fields are missing is not descriptive and there is no indication in the current documentation (that I can see anyway) that would indicate these fields are required.

* Update annotations.md

Update required json body fields to only include fields that are actually required.

* Add required field in Swagger

Co-authored-by: Sofia Papagiannaki <1632407+papagian@users.noreply.github.com>

docs/sources/developers/http_api/annotations.md

@@ -122,6 +122,10 @@ See note in the [introduction]({{< ref "#annotations-api" >}}) for an explanatio
 | ------------------ | ----------------------- |
 | annotations:create | annotations:type:<type> |
 
+**Required JSON Body Fields**
+
+- `text`: description of the annotation.
+
 **Example Request**:
 
 ```http

pkg/api/dtos/annotations.go

@@ -8,6 +8,7 @@ type PostAnnotationsCmd struct {
 	PanelId      int64  `json:"panelId"`
 	Time         int64  `json:"time"`
 	TimeEnd      int64  `json:"timeEnd,omitempty"` // Optional
+	// required: true
 	Text string           `json:"text"`
 	Tags []string         `json:"tags"`
 	Data *simplejson.Json `json:"data"`

public/api-merged.json

@@ -14150,6 +14150,7 @@
     },
     "PostAnnotationsCmd": {
       "type": "object",
+      "required": ["text"],
       "properties": {
         "dashboardId": {
           "type": "integer",

public/api-spec.json

@@ -12099,6 +12099,7 @@
     },
     "PostAnnotationsCmd": {
       "type": "object",
+      "required": ["text"],
       "properties": {
         "dashboardId": {
           "type": "integer",