Add RestTestClient

Fixes spring-projectsgh-31275

Signed-off-by: Rob Worsnop <rworsnop@gmail.com>

Author: rworsnop

framework-docs/modules/ROOT/nav.adoc

@@ -348,6 +348,7 @@
 *** xref:testing/testcontext-framework/support-classes.adoc[]
 *** xref:testing/testcontext-framework/aot.adoc[]
 ** xref:testing/webtestclient.adoc[]
+** xref:testing/resttestclient.adoc[]
 ** xref:testing/mockmvc.adoc[]
 *** xref:testing/mockmvc/overview.adoc[]
 *** xref:testing/mockmvc/setup-options.adoc[]