Can't start dev container: multi-python is deprecated

# Bug

Dev container fails to start. Container dependency in [.devcontainer/Dockerfile](https://github.com/art049/odmantic/blob/master/.devcontainer/Dockerfile) called [multi-python](https://github.com/fkrull/docker-multi-python) is deprecated. Failure during container start gives "failed to find package fkrull/docker-multi-python" as the cause. A visit to [the repo](https://github.com/fkrull/docker-multi-python) shows it's been deprecated and removed.

### Current Behavior

In VS Code:
1. Download extension Dev Containers (as suggested in [Contributing](https://art049.github.io/odmantic/contributing/) docs)
2. Cmd + Shift + P
3. Choose "Dev Containers: Clone Repository in Container Volume..."
4. Container start fails

### Expected behavior

Odmantic codebase starts in Docker container

### Environment

- ODMantic version: ... 0.9.2
- MongoDB version: ... latest (probably 7.0)
- Pydantic infos (output of `python -c "import pydantic.utils; print(pydantic.utils.version_info())`):
Cannot run in container.

Start with .devcontainer/Dockerfile and the Contributing documentation, then reproduce the failure using VS Code's Dev Containers: Clone Repository in Container Volume flow. Identify a supported replacement for the deprecated multi-python dependency and verify that the ODMantic codebase starts successfully in the dev container.

Written by the indexing model from the issue text.