Draft: defect and supercell setup utilities

We want to implement new defect setup utilities in ase.build. Those will be the following:

• Vacancy and antisite generation
• Intrinsic defects and extrinsic dopants
• Interstitial defects
• Defect complexes

It would be most natural to implement it in ase.build.defects. Furthermore, we want to extend ase.build.supercell with additional functionalities:

• Automatic supercell generation with broken symmetries
• 1D, 2D, and 3D support
• Compability with ase.build.defects
• General supercell setup of type LxMxN

Some things to address with this merge request:

• spglib and other dependencies
• what should we do with the ase.spacegroup.wyckoff module?

Documentation tasks:

• Write documentation page
• Automatic generation of the documentation images
• Add ADAQ citation