Provide direction-dependent calibration in the Mid imaging pipeline

Direction-dependent calibration is necessary to ensure the science capability of SKA imaging for a number of the Mid bands (potentially all). As a potentially computationally expensive and time-consuming step, ensuring that the Mid self-calibration pipelines provide this capability is crucial in order to ensure we can test and scale the pipeline appropriately for AA2+.

• Implement direction-dependent calibration, i.e. predict and calibrate different parts of the sky separately
• Provide results of test runs (with profiling information), test data and parameter settings used to demonstrate the direction-dependent pipeline in SI (https://confluence.skatelescope.org/display/SWSI/Scaling+progress+report)
• Apply direction-dependent calibration to imaging, i.e. split image into facets and demonstrate that different calibration solutions can be applied to facets

The MID self-calibration pipeline was extended to use DDECal from DP3 and facets that are being processed by WSClean. Relevant data structures and code for handling facets were written to enable this functionality. At the moment, the DD MID pipeline creates square facets, assigns sources from the initial sky model and creates files required by the WSClean. The directional independent MID pipeline was also modified to extend the number of parameters the user can adjust for feature SP-3477 and for benchmarking relevant to KR4. In parallel, the development on a code that creates facets based on Voronoi tessellation was written. Details are on the confluence page https://confluence.skatelescope.org/display/SE/HIP-614%3A+Plotting+Voronoi+tessellation+diagrams+using+Scipy+data.
The DD MID self-calibration pipeline was tested on a simulated AA2 dataset generated in PI18. At the moment, the DD MID pipeline creates a regular grid of square facets, matches sources from the initial sky model to their respective facets and from there provides the information required by DP3 and WSClean to perform direction-dependent calibration and imaging. The results are described on the confluence page https://confluence.skatelescope.org/display/SE/HIP-638%3A+Attempts+to+obtain+a+reasonable+image+of+the+AA2+Mid+field+with+DDECal. After some initial problems given by unfamiliarity with the software these problems were fixed and the pipeline is now producing reasonable results. 
Documentation of the MID self-calibration was updated accordingly (https://developer.skao.int/projects/ska-telescope-ska-sdp-wflow-mid-selfcal/en/latest/pipeline_dd.html).