workflow usable by all tenants using multitenancy

## Feature Request

### Problem Overview
Our company has a different multitenancy setup than Elsa. We both want workflows than can only be configured and triggered by a single tenant and generic workflows that we define and should usable for any tenant, but would still have access to the information of that user tenant. Currently we are bypassing this by storing the tenant code as a variable in the workflow instance.

### Proposed Solution
A workflow with no tenant of its own, but usable by any tenant that is authenticated.

### Alternative Solutions
Disabling multitenancy and handling tenants with variables and our own authorization solution.

### Use Cases
We provide SaaS to different customers that use hardcoded workflows as part of the service but also want to configure their own for their specific use cases.