Helper for controlDict with functions

It would be better and very easy to use a FileHelper for the controlDict file.

We should have a good API to use functions:

https://www.openfoam.com/documentation/guides/v2112/doc/guide-function-objects.html

We have in our solvers:

code_control_dict_functions = dedent(
    """
    functions
    {
        minmaxdomain
        {
            type fieldMinMax;
            //type banana;

            libs ("libfieldFunctionObjects.so");

            enabled true;

            mode component;

            writeControl timeStep;
            writeInterval 1;

            log true;

            fields (p U);
        }
    };
"""
)

and

code_control_dict_functions = dedent(
    """
    functions
    {
        #includeFunc solverInfo
        #includeFunc streamlines
    }
"""
)