add(gitea-api): creation for issues, milestones and comments

This implements the post api functions for issues, milestones and
comments which are added to the gitea repository.

internal/gitea/comment.go

@@ -70,3 +70,26 @@ func (gitea *Gitea) UpdateComment(repo Repository, comment Comment) error {
 	}
 	return nil
 }
+
+func (gitea *Gitea) NewComment(repo Repository, issue Issue, comment Comment) (Comment, error) {
+	url := fmt.Sprintf("%s/repos/%s/issues/%d/comments", gitea.Url(), repo.Full_name, issue.Id)
+	payload, err := json.Marshal(&map[string]interface{}{
+		"body": comment.Body,
+	})
+	var res Comment
+	if err != nil {
+		return res, err
+	}
+	response, err := http.Post(url, "application/json", bytes.NewBuffer(payload))
+	if err != nil {
+		return res, nil
+	}
+	defer response.Body.Close()
+	decoder := json.NewDecoder(response.Body)
+	// NOTE: remove this if I do not want to store everything from the json result in the struct
+	decoder.DisallowUnknownFields() // remain if every field shall be extracted
+	if err = decoder.Decode(&res); err != nil {
+		return res, err
+	}
+	return res, nil
+}