feat: add stochastic fem example

[moe-ad]

Description

This PR will add an example to the PyMAPDL documentation

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have reviewed my changes before submitting this pull request.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.08%. Comparing base (e83f46c) to head (e03e38d).
Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3648   +/-   ##
=======================================
  Coverage   87.08%   87.08%           
=======================================
  Files         187      187           
  Lines       14679    14694   +15     
=======================================
+ Hits        12783    12797   +14     
- Misses       1896     1897    +1