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/milestone.go

@@ -72,3 +72,29 @@ func (gitea *Gitea) UpdateMilestone(repo Repository, milestone Milestone) error
 	}
 	return nil
 }
+
+func (gitea *Gitea) NewMilestone(repo Repository, milestone Milestone) (Milestone, error) {
+	url := fmt.Sprintf("%s/repos/%s/milestones", gitea.Url(), repo.Full_name)
+	payload, err := json.Marshal(&map[string]interface{}{
+		"description": milestone.Description,
+		"due_on":      milestone.Due_on,
+		"state":       milestone.State,
+		"title":       milestone.Title,
+	})
+	var res Milestone
+	if err != nil {
+		return res, err
+	}
+	response, err := http.Post(url, "application/json", bytes.NewBuffer(payload))
+	if err != nil {
+		return res, err
+	}
+	defer response.Body.Close()
+	decoder := json.NewDecoder(response.Body)
+	// NOTE: remove this if I do not want to stare 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
+}