add(gitea-api): issue and milestone updating

This implements the api patches for updating an issue or milestone for a
given repository and issue or milestone. WIP for #1.

internal/gitea/milestone.go

@@ -1,6 +1,7 @@
 package gitea
 
 import (
+	"bytes"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -53,3 +54,21 @@ func (gitea *Gitea) GetMilestone(repo Repository, id uint) (Milestone, error) {
 	}
 	return milestone, nil
 }
+
+func (gitea *Gitea) UpdateMilestone(repo Repository, milestone Milestone) error {
+	url := fmt.Sprintf("%s/repos/%s/milestones/%d", gitea.Url(), repo.Full_name, milestone.Id)
+	var payload map[string]interface{}
+	payload["description"] = milestone.Description
+	payload["due_on"] = milestone.Due_on
+	payload["state"] = milestone.State
+	payload["title"] = milestone.Title
+	json, err := json.Marshal(&payload)
+	if err != nil {
+		return err
+	}
+	_, err = http.NewRequest(http.MethodPatch, url, bytes.NewBuffer(json))
+	if err != nil {
+		return err
+	}
+	return nil
+}