Enable testing with local MongoDB and MLFlow servers

[RemiLehe]

In order to enable local development and testing, we should add instructions to start local MongoDB and MLFlow servers (with ephemeral data), e.g. by running docker containers:

docker run -p 127.0.0.1:5000:5000 ghcr.io/mlflow/mlflow mlflow server --host 0.0.0.0
docker run -p 127.0.0.1:27017:27017 mongo

and modify the code to be able to fill up the mongoDB database with some example data and run using these resources.

[RemiLehe]

In order to use the local mflow server, the config.yaml needs to be modified like this:

mlflow:
  tracking_uri: "http://localhost:5000"