ManagementWebServerFactoryCustomizer and ManagementErrorPageCustomizer should not have the same order

[snicoll]

This seems to have worked thus far by accident. They're both at order 0 and one is clearing the error pages while the other is registering an error page.

Flagging for team-attention as I am not sure where to fix this.

[wilkinsona]

I think we should fix it in 3.4.x and later.