Replace blackfriday with goldmark

This change replaces the unmaintained blackfriday markdown renderer with the
goldmark renderer.
The goal is to have wider support for more markdown extensions and ideally
have a better solution for mermaid transformation via extensions as well.

pkg/confluence/api.go

@@ -555,7 +555,7 @@ func (api *API) UpdatePage(page *PageInfo, newContent string, minorEdit bool, ne
 			"labels": labels,
 			// Fix to set full-width as has changed on Confluence APIs again.
 			// https://jira.atlassian.com/browse/CONFCLOUD-65447
-			// 
+			//
 			"properties": map[string]interface{}{
 				"content-appearance-published": map[string]interface{}{
 					"value": appearance,