Log failed template parsing reasons to console.

When using the API, you can fail to parse but be unaware of why.

Provide that context on the console.

src/github.com/matrix-org/go-neb/services/alertmanager/alertmanager.go

@@ -129,6 +129,10 @@ func (s *Service) Register(oldService types.Service, client *gomatrix.Client) er
 			// validate the plain text template is valid
 			_, err := text.New("textTemplate").Parse(templates.TextTemplate)
 			if err != nil {
+				log.WithFields(log.Fields{
+					"line":        err.line,
+					"description": err.description,
+				}).Info("plain text Template Error")
 				return fmt.Errorf("plain text template is invalid")
 			}
 		}
@@ -136,6 +140,10 @@ func (s *Service) Register(oldService types.Service, client *gomatrix.Client) er
 			// validate that the html template is valid
 			_, err := html.New("htmlTemplate").Parse(templates.HTMLTemplate)
 			if err != nil {
+				log.WithFields(log.Fields{
+					"line":        err.line,
+					"description": err.description,
+				}).Info("HTML Template Error")
 				return fmt.Errorf("html template is invalid")
 			}
 		}