[WIP] Add DiscreteWeibull

[aleicazatti]

Description

Add DiscreteWeibull distribution. Issue #236

WIP:

• Tests for this distribution are not implemented yet.
• _fit_moments function is not implemented yet. "The moments of this distribution do not have closed forms and therefore the parameters cannot be estimated by ordinary techniques" https://ieeexplore.ieee.org/document/44179
• plot_ppf method raises a RuntimeWarning: divide by zero encountered in log return np.ceil(((np.log(1 - p) / np.log(self.q)) ** (1 / self.beta)) - 1)

Checklist

• Code style is correct (follows pylint and black guidelines)
• New features are properly documented (with an example if appropriate)
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)

[aloctavodia]

"DiscreteWeibull" is missing from init_vals https://github.com/arviz-devs/preliz/blob/33e9a74df3ee364c164c0984649de4f24cc2c649/preliz/internal/distribution_helper.py