feat(saml): Add auth0 provider icon

src/sentry/static/sentry/less/auth.less

@@ -51,6 +51,10 @@ section.org-login {
     background-image: url(../images/auth-providers/onelogin.png);
   }
 
+  &.auth0 {
+    background-image: url(../images/auth-providers/auth0.png);
+  }
+
   &.okta {
     background-image: url(../images/auth-providers/okta.png);
   }