[KSW-Guides] Defining an input schema for Workflows

Page: https://github.com/kiegroup/kogito-docs/blob/main/serverlessworkflow/modules/ROOT/pages/core/defining-an-input-schema-for-workflows.adoc

In this guide, we should instruct the user on how to create a JSON Schema file, add it to the Serverless Workflow project, and refer to it in the workflow definition. The application should generate an OpenAPI file (http://localhost/q/swagger-ui) referencing this schema file, so users will be able to correctly define the input data for their workflows.