Consider providing testing beans for @SpringBootTest when used with mock web apps

[philwebb]

See spring-projects/spring-graphql#75 and #26146 for examples of where it would be nice to have more client beans automatically configured.

[philwebb]

This issue is about taking the table in #26146 (comment) and improving the defaults so that WebTestClient beans are available. #26146 remains about documenting the current status.