Finalize release notes for 4.0.0-beta1

[michaelosthege]

This list will hopefully shrink fast; ideally without growing the sections below.

Closes #5149

[codecov]

Codecov Report

Merging #5202 (cc3129d) into main (c22859d) will increase coverage by 1.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5202      +/-   ##
==========================================
+ Coverage   78.13%   79.17%   +1.04%     
==========================================
  Files          88       88              
  Lines       14181    14346     +165     
==========================================
+ Hits        11080    11359     +279     
+ Misses       3101     2987     -114     

Impacted Files	Coverage Δ
pymc/__init__.py	96.00% <100.00%> (-0.08%)	⬇️
pymc/step_methods/hmc/integration.py	78.84% <0.00%> (-3.85%)	⬇️
pymc/backends/report.py	89.51% <0.00%> (-2.10%)	⬇️
pymc/parallel_sampling.py	86.33% <0.00%> (-1.00%)	⬇️
pymc/distributions/dist_math.py	86.78% <0.00%> (-0.92%)	⬇️
pymc/step_methods/hmc/nuts.py	95.00% <0.00%> (-0.63%)	⬇️
pymc/tests/sampler_fixtures.py	90.76% <0.00%> (-0.48%)	⬇️
pymc/model.py	83.26% <0.00%> (-0.05%)	⬇️
pymc/backends/arviz.py	89.51% <0.00%> (-0.05%)	⬇️
... and 18 more

[michaelosthege]

@bwengals can you check the diff to make sure all breaking changes in the GP module are mentioned? (I think it's now requiring kwargs in a few places?)

[ricardoV94]

Here is another one: #5260 Edited it already