Update cloudpickle reqs for SDK-only install

[cjao]

This is a followup to 1873. The full install already allows >=2.0.0.

• I have added the tests to cover my changes.
• I have updated the documentation and CHANGELOG accordingly.
• I have read the CONTRIBUTING document.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (d94bdaf) 84.43% compared to head (9af83a8) 84.51%.
Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1898      +/-   ##
===========================================
+ Coverage    84.43%   84.51%   +0.08%     
===========================================
  Files          294      295       +1     
  Lines        14389    14476      +87     
  Branches       195      195              
===========================================
+ Hits         12149    12235      +86     
- Misses        2106     2107       +1     
  Partials       134      134              

Flag	Coverage Δ
Dispatcher	92.33% <ø> (ø)
Functional_Tests	51.43% <65.42%> (+0.11%)	⬆️
SDK	79.54% <94.39%> (+0.23%)	⬆️
UI_Backend	84.73% <ø> (ø)
UI_Frontend	73.35% <ø> (ø)