zfit/zfit: Gaussian KDE, BreitWigner and correlation

Add Kernel density estimation for 1 dimension. Major Features and Improvements add correlation method to FitResult Gaussian (Truncated) Kernel Density Estimation in one dimension zfit.pdf.GaussianKDE1DimV1 implementation with fixed and adaptive bandwidth added as V1. This is a feature that needs to be improved and feedback is welcome Non-relativistic Breit-Wigner PDF, called Cauchy, implementation added. Breaking changes change human-readable name of Gauss, Uniform and TruncatedGauss to remove the '_tfp' at the end of the name Bug fixes and small changes fix color wrong in printout of results, params packaging: moved to pyproject.toml and a setup.cfg mainly, development requirements can be installed with the dev extra as (e.g.) pip install zfit[dev] Fix shape issue in TFP distributions for partial integration change zfit internal algorithm (zfit_error) to compute error/intervals from the profile likelihood, which is 2-3 times faster than previous algorithm. add from_minuit constructor to FitResult allowing to create it when using directly iminuit fix possible bias with sampling using accept-reject Requirement changes pin down cloudpickle version (upstream bug with pip install) and TF, TFP version