New module for pyfluent module constants

[mkundu1]

Should we move the pyfluent module constants to a separate module ansys.fluent.core.constants? This could fix the circular dependency issue we often see while importing constants into modules directly or indirectly imported in ansys.fluent.core.__init__. E.g., try to import one of the constants in src\ansys\fluent\core\launcher\standalone_launcher.py.

We still want to preserve the usage: ansys.fluent.core.<CONSTANT_NAME>.