Update Gradle examples to use configurations for dependencies that are Gradle 7-compatible

[brneto]

The Spring REST Docs documentation suggests add spring-restdocs-mockmvc dependency in the testCompile configuration.

Gradle 7.2 do not use this configuration anymore but instead testCompileOnly also with dependency spring-restdocs-webtestclient it is working only in the testImplementation configuration.

See:
https://gitter.im/spring-projects/spring-restdocs?at=6123547ceb72173430e02917
https://gitter.im/spring-projects/spring-restdocs?at=61235b29aa48d1340c298457

[wilkinsona]

@brneto Thanks for raising this. Spring REST Docs is managed as a separate project. I'll transfer this issue so it's in the right place.

[brneto]

@wilkinsona As done before I'm happy to help in this documentation update if you may want. Please, just point the direction and I can do the rest.

[wilkinsona]

On closer inspection, this was already done as part of #719.