LoadFlowDefaultParametersLoader cannot be used to set default provider parameters

[HugoKulesza]

Describe the current behavior

LoadFlowDefaultParametersLoader is supposed to allow a project to add loadflow parameters as a JSON file in the classpath, that are loaded on top of hardcoded default parameters and can then still be overridden by the user config.yml file.
This behaviour does not work for loadflow provider parameters that we can define as extensions in the JSON file, because they are completely recreated with default values if any such parameter is present in the config.yml of the user.

Describe the expected behavior

We should be able to change loadflow provider default parameters using this mecanism without this new default value being removed of provider parameters if a user has its own parameters file.

Describe the steps

No response

Environment

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Relevant Log Output

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Extra Information

No response