Refactor E2E tests and configuration format

- Replaced `easymapping` configuration with `containers` for better maintainability and clarity.
- Introduced `DockerComposeFixture` class in `utils.py` to manage Docker Compose lifecycle and smart build strategy.
- Enhanced YAML-to-environment variable conversion in `ContainerEnv` for dynamic configuration support.
- Updated HAProxy configurations and test fixtures to reflect the new format.
- Improved test coverage for YAML parsing, environment variable handling, and HAProxy config generation.

tests_e2e/static/README.md

@@ -79,13 +79,10 @@ stats:
   password: password
   port: 1936
 
-easymapping:
-  - port: 443
+containers:
+  "host1.local:443":
+    ip: ["container:8080"]  # Can also be IP:PORT for external backends
     ssl: true
-    hosts:
-      host1.local:
-        containers:
-          - container:8080  # Can also be IP:PORT for external backends
 ```
 
 See `conf/` directory for complete examples.