To avoid copy/paste of `TestMailServer` in other projects (e.g. samples or Java DSL), port `TestMailServer` from SI-5.0 to the shared `spring-integration-test` module That allows to avoid unexpected SI-5.0 dependency in samples for SI-4.3
To avoid copy/paste of `TestMailServer` in other projects (e.g. samples or Java DSL), port `TestMailServer` from SI-5.0 to the shared `spring-integration-test` module That allows to avoid unexpected SI-5.0 dependency in samples for SI-4.3