Make mlflow.yml configuration file optional

[Galileo-Galilei]

Description

Before using kedro-mlflow in a kedro project, it is needed to create a configuration file with kedro mlflow init command.

Context

It will make plugin installation easier, since it will work "out of the box". Additionnally, I've found that many users don't modify this file, except eventually the mlflow_tracking_uri.

Possible Implementation

Instead of raising error, raise a warnign and instantiate a default KedroMlflowConfig in the after_context_created hook:

kedro-mlflow/kedro_mlflow/framework/hooks/mlflow_hook.py

Lines 60 to 65 in df8430e

	try:
	conf_mlflow_yml = context.config_loader.get("mlflow*", "mlflow*/**")
	except MissingConfigException:
	raise KedroMlflowConfigError(
	"No 'mlflow.yml' config file found in environment. Use ``kedro mlflow init`` command in CLI to create a default config file."
	)