Add Outbox pattern examples and IT tests #1579

Context

Looking the following documentation: https://docs.dapr.io/developing-applications/building-blocks/state-management/howto-outbox (looks old, I am opening a pull request to update the Java examples) we have way to use Outbox pattern through Dapr APIs.

Problem

We do not have a example in the Spring Boot project (for Spring users) or even a integration test to be sure that everything are working.

Proposal

• Add an example for Spring Boot
• Add integration test for Outbox