`SuperConWorkChain`: add flexibility in how to solve the Migdal-Eliashberg equation

[mbercx]

From @ymzhang0, commented in the define method of the SuperConWorkChain:

TODO: We can choose how we solve the Migdal-Eliashberg equations. We can have another input port do_fbw such that if we want to do a full-bandwidth calculation, we can set it to true. We can have another input port do_ir such that if we want to do solve it in the intermediate representation space, we can set it to true.