add service to Ferdium (multi messenger)

[heylix]

Describe the problem

https://ferdium.org/ is the continuation of the Ferdi multi messenger. Cinny maybe can be used as a service there, as Element is already in there.

Describe the solution you'd like

ideally there'd be a self contained local Cinny inside of the container.

Alternatives considered

custom service, which I set up with my self hosted Cinny server.

Additional context

https://github.com/ferdium/ferdium-recipes