oauth/m2m: make "token fetched successfully" a debug log (#306)

The log is quite repetitive, and as we use this sql driver in our
customer-facing product where customers see logs, the extra log seems
like spam to customers. I think it would be nice to have it as debug log
instead of info.

Author: vikrantpuppala

auth/oauth/m2m/m2m.go

@@ -57,7 +57,7 @@ func (c *authClient) Authenticate(r *http.Request) error {
 
 	c.tokenSource = GetTokenSource(config)
 	token, err := c.tokenSource.Token()
-	log.Info().Msgf("token fetched successfully")
+	log.Debug().Msgf("token fetched successfully")
 	if err != nil {
 		log.Err(err).Msg("failed to get token")