Spring Security Add ExceptionHandlingSpec.defaultAuthenticationEntryPointFor()

We should allow for custom ServerAuthenticationEntryPoint to be configured via ServerHttpSecurity.ExceptionHandlingSpec.

ExceptionHandlingConfigurer provides:

defaultAuthenticationEntryPointFor(AuthenticationEntryPoint, RequestMatcher)

We should align ServerHttpSecurity.ExceptionHandlingSpec and provide:

defaultAuthenticationEntryPointFor(ServerAuthenticationEntryPoint, ServerWebExchangeMatcher)