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