Previously, the documentation did not describe how to combine
multiple security components when one component's
WebSecurityConfigurerAdapter or SecurityWebFilterChain would cause
the other components' beans of the same type to back off.

This commit adds a note that such cases should be handled by the user
defining their own WebSecurityConfigurerAdapter or
SecurityWebFilterChain that configures the use of all of the
components as required.

Closes gh-18507