Ability to disable master node deployment

This issue is to discuss more in regards to feasibility of these features and to discuss how heavy the involvement of lunni is planned to be, in regards to custom logics beyond simple stack deployments.

---

Following our discussion in #32 about the planned custom backend logic, I'd like to suggest a feature to globally configure deployment constraints to prevent stacks from being deployed on Docker Swarm manager nodes.

Currently, achieving this requires defining constraints on each individual stack. A cluster-wide setting to automatically apply these constraints would simplify management and offer a more consistent experience.

For reference, we can refer to swiftwave which provides a similar feature (see: https://swiftwave.org/docs/dashboard/manage-servers ) where deployment to specific nodes or roles can be globally controlled.

As we discussed in #32 regarding volume management, perhaps a similar mechanism could be implemented, where deployment constraints are automatically applied to all deployed stacks within the cluster. This would be a more efficient and manageable solution than configuring individual stacks.