Create new endpoints to retrieve workflows and schema

On Backstage PoC it was identified the need for an endpoint retrieve all workflows with details and intput/output schemas.

The workflows are used to be listed in the Backstage UI and the schema is used to render forms to start workflow instances.

The idea it to provide new endpoints under processes-management addon, since they are not domain endpoints.

/processes (list of workflows ids)
/processes/{id} (details of workflow including the schemas)

This is important for use cases where it is required listing possible workflow the application holds.