add option to display rank plots instead of trace

[aloctavodia]

Integrates rank plots into plot_trace via the new keyword kind, defaults to kind=trace

Checklist

• Follows official PR format
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• New features are properly documented (with an example if appropriate)?
• Includes new or updated tests to cover the new feature
• Code style correct (follows pylint and black guidelines)
• Changes are listed in changelog

kind=rank_vlines

kind=rank_bars

[codecov]

Codecov Report

Merging #1134 into master will increase coverage by 0.12%.
The diff coverage is 94.28%.

@@            Coverage Diff             @@
##           master    #1134      +/-   ##
==========================================
+ Coverage   92.68%   92.81%   +0.12%     
==========================================
  Files          93       93              
  Lines        9073     9181     +108     
==========================================
+ Hits         8409     8521     +112     
+ Misses        664      660       -4     

Impacted Files	Coverage Δ
arviz/plots/traceplot.py	97.33% <75.00%> (-1.26%)	⬇️
arviz/plots/backends/bokeh/traceplot.py	95.97% <93.33%> (-0.43%)	⬇️
arviz/plots/backends/matplotlib/traceplot.py	99.15% <100.00%> (+0.06%)	⬆️
arviz/data/inference_data.py	81.88% <0.00%> (-1.26%)	⬇️
arviz/utils.py	90.00% <0.00%> (-0.96%)	⬇️
arviz/data/io_pystan.py	98.67% <0.00%> (-0.40%)	⬇️
arviz/stats/stats.py	96.32% <0.00%> (-0.21%)	⬇️
arviz/rcparams.py	93.10% <0.00%> (ø)
arviz/plots/backends/__init__.py	29.11% <0.00%> (ø)
arviz/plots/backends/bokeh/rankplot.py	93.33% <0.00%> (+1.66%)	⬆️
... and 2 more

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[ahartikainen]

LGTM

Do we need one example for the gallery?

[ahartikainen]

Also changelog needs update