Extend flexibility in input var plotting functions

Summary

This MR introduces the following changes

• using **kwargs in the plotting functions, allowing to specify any parameter that is understood in the plotting API (in this case the histogram_plot class) in the config file for plotting
• removed the check_kwargs_var_plots function
• moved the "kwargs translation" (for backwards compatibility) to the high-level functions in plot_input_vars.py (--> kwargs are translated to new naming right away, such that the new naming is used consistently afterwards)
• making histogram_plot functions less verbose (logger.info -> logger.debug), to reduce stdout in large plotting scripts
• adding a script that converts the "Parameters" section of certain docstrings to markdown tables. The resulting files can then be used in the docs (using our placeholder syntax we introduced in !476 (merged))

Example

With this change, you can now e.g. remove the ATLAS branding from the input var plots by simply adding atlas_brand: "" to the plot_settings in the config:

--> -->

Relates to the following issues

• #147 (closed)

Conformity

• Changelog entry
• Documentation
• Development guidelines
• Style guides