feat: Set string settings with allowed values via string constants

[mkundu1]

The enumerated values are exposed as constant attributes of the instance. Please see the unittest for usage.

There is already an attribute allowed-values-with-display-text in settings API to fetch all possible allowed values which has been added to the static-info (Fluent PR 599447).

Below is the fragment of generated class:

class model_2(String, AllowedValuesMixin):
    """
    Viscous Model.
    """
    _version = '261'
    fluent_name = 'model'
    _python_name = 'model'
    LAMINAR = _FlConstant('laminar')
    MIXING_LENGTH = _FlConstant('mixing-length')
    KE1E = _FlConstant('ke1e')
    INVISCID = _FlConstant('inviscid')
...

TODO: doc update

[prmukherj]

@mkundu1, existing tests suggest that something has gone wrong.

[mkundu1]

Validation against all possible allowed values during set_state is now possible in the client side, will add it.

[hpohekar]

Validation against all possible allowed values during set_state is now possible in the client side, will add it.

That's great! Thank you.