Add docker swarm diagram for dokploy cluster feature

[anav5704]

What problem will this feature address?

There is no diagram that shows how the dokploy cluster feature works at a high level. The dokploy discord has frequent questions and problems regarding clusters.

Describe the solution you'd like

Add an architecture diagram that shows how dokploy manages a docker swarm cluster (manager nodes vs worker nodes).

Describe alternatives you've considered

Additional context