Configure oauth2client in Reactive OAuth2 client auto-configuration

[mbhave]

This issue in Spring Security added oauth2client to the webflux configuration so that it is consistent with the servlet counterpart. Following #17949, Spring Boot explicitly configures a bean of type SecurityWebFilterChain, instead of relying on the one from Spring Security, so that ReactiveManagementWebSecurityAutoConfiguration can back off in the presence of OAuth2.

We need to update the SecurityWebFilterChain bean to include configuration for oauth2client().

[mbhave]

Since the Spring Security change was made in 5.2, we should do this in 2.2.