Reinstate support for REST Assured now that it supports Groovy 5

[snicoll]

https://github.com/rest-assured/rest-assured/wiki/ReleaseNotes60

We first need a new release of Spring RESTDocs, see spring-projects/spring-restdocs#1020

We may want reviewing #47686 as well.

[wilkinsona]

Boot's support for REST Assured was very light, only auto-configuring Spring REST Docs' REST Assured support. That support may not be reinstated. It depends on demand and the possibility of RestTestClient support being added instead. Closing, for now at least. We can re-open if spring-projects/spring-restdocs#1020 happens in the future.