Use the generic class for TUI menus inserted at runtime

[mkundu1]

An example of dynamic menu is the adjoint/observable menu in Fluent. During the static class generation in codegen, it doesn't have any child, so a bound method is generated for it. During runtime, new child menus (like create, edit) are added at adjoint/observable level in Fluent. Earlier the only way to execute /adjoint/observable/create in Fluent was to pass the child menu create as argument of adjoint.observbale method from PyFluent, i.e. session.solver.tui.adjoint.observable("create", '"<type>"', '"<name>"').

In this PR, dynamic menus are identified in Fluent and corresponding objects of generic type inserted in PyFluent at runtime:

>>> session.solver.tui.adjoint # object of explicit type encoded during codegen
<ansys.fluent.core.solver.tui.main_menu.adjoint object at 0x000002B468FF08B0>
>>> session.solver.tui.adjoint.observable # object of generic type created at runtime
<ansys.fluent.core.services.datamodel_tui.TUIMenuGeneric object at 0x000002B468FF0640>
>>> session.solver.tui.adjoint.observable.create('"<type>"', '"<name>"')