chore: Use top-level kepler_model python package

[sthaha]

The PR refactors the code base to follow python packaging guidelines - https://packaging.python.org/en/latest/guides/writing-pyproject-toml/ The changes are as follows

• all src/* are moved to src/kepler_model so that from kepler_model.X import Y works (as guideline recommends)
• All executable python scripts are generated using project.script. These scripts essentially call the kepler_model.<component>.run function
• All sys.path.append (hacks) are removed
• missing __init__.py has been added to all package
• dockerfile changes are made to support the modifications needed by above

Please note further cleanup / optimisations may be possible but can be done in a follow up patch.

[vprashar2929]

@sthaha adding a description?