In Python, the constructor for FunctionCallContent has a name string and argument string.

In .NET, the name is split into functionName and pluginName and the argument variable is an object.

To align, the possible should be possible:

FunctionCallContent(
    function_name="get_user_allergies",
    plugin_name="User",
    id="0001",
    arguments={"username": "laimonisdumins"}
)