...along with Spring Cloud Finchley.M6, and Spring Cloud Stream Elmhurst.M4

* Update Spring Security policy settings as well as default dummy accounts using new APIs, and new reactive APIs.
* Update custom Thymeleaf authorization processor to find SecurityContext inside the exchange. (Still no thymeleaf-extras-springsecurity5 WebFlux support)
* Replace custom Spring Cloud Gateway filter with comment because code was contributed to the project.
* Patch some unit tests that broke due to constructor settings for Selenium.