Replace Read Only Editor role with ViewersCanEdit setting (#10166)

* removes readonly editor role

* adds viewersCanEdit setting

This enable you to allow viewers to edit/inspect
dashboards in grafana in their own browser without
allowing them to save dashboards

* remove read only editor option from all dropdowns

* migrates all read only viewers to viewers

* docs: replace readOnlyEditor with viewersCanEdit

docs/sources/http_api/auth.md

@@ -100,7 +100,7 @@ Authorization: Bearer eyJrIjoiT0tTcG1pUlY2RnVKZTFVaDFsNFZXdE9ZWmNrMkZYbk
 
 **Example Request**:
 
-```http
+```http
 DELETE /api/auth/keys/3 HTTP/1.1
 Accept: application/json
 Content-Type: application/json