✨(backend) introduce general recording worker concepts

Introducing a new worker service architecture. Sorry for the long commit.
This design adheres to several key principles, primarily the  Single
Responsibility Principle. Dependency Injection and composition are
prioritized over inheritance, enhancing modularity and maintainability.

Interactions between the backend and external workers are encapsulated in
classes implementing a common `WorkerService` interface. I chose Protocol
over an abstract class for agility, aligning closely with static typing
without requiring inheritance. Each `WorkerService` implementation can
independently manage recordings according to its specific requirements.
This flexibility ensures that adding a new worker service, such as for
LiveKit, can be done without any change to existing components.

Configuration management is centralized in a single `WorkerServiceConfig`
class, which loads and provides all settings for different worker
implementations, keeping configurations organized and extensible. The worker
service class itself handles accessing relevant configurations as needed,
simplifying the configuration process.

A basic dictionary in Django settings acts as a factory, responsible for
instantiating the correct worker service based on the client's request mode.
This approach aligns with Django development conventions, emphasizing
simplicity. While a full factory class with a builder pattern could provide
future flexibility, YAGNI (You Aren't Gonna Need It) suggests deferring
such complexity until it’s necessary.

At the core of this design is the worker mediator, which decouples worker
service implementations from the Django ORM and manages database state
according to worker state. The mediator is purposefully limited in
responsibility, handling only what’s essential. It doesn’t instantiate
worker services directly; instead, services are injected via composition,
allowing the mediator to manage any object conforming to the `WorkerService`
interface. This setup preserves flexibility and maintains a clear
separation of responsibilities. The factory create worker services,
the mediator runs it.

(sorry for this long commit)

src/backend/pyproject.toml

@@ -57,6 +57,7 @@ dependencies = [
     "whitenoise==6.7.0",
     "mozilla-django-oidc==4.0.1",
     "livekit-api==0.7.0",
+    "aiohttp==3.10.10",
 ]
 
 [project.urls]