GW-BSE calculation with Abinit

[tatha0003]

Summary

Include a summary of major changes in bullet points:

• Feature:
• GW-BSE calculation with Abinit
• GW workflow includes convergence tests for important parameters like the number of empty bands
• BSE workflow has the option to choose model dielectric function or full screening matrix to use
• BSE workflow includes convergence with respect to the number of k-points.

Additional dependencies introduced (if any)

No additional dependencies

TODO (if any)

Need to move /atomate2/abinit/sets/factories.py to abipy/abio/factories.py