Make steplength settable again in IES

[dafeda]

Issue
Resolves #5062

Approach
Short description of the approach

Pre review checklist

• Added appropriate release note label
• PR title captures the intent of the changes, and is fitting for release notes.
• Commit history is consistent and clean, in line with the contribution guidelines.
• Updated documentation
• Ensured new behaviour is tested

Adding labels helps the maintainers when writing release notes. This is the list of release note labels.

[codecov-commenter]

Codecov Report

Merging #5075 (c4b2fa0) into main (bca8ad6) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #5075      +/-   ##
==========================================
+ Coverage   71.85%   71.90%   +0.04%     
==========================================
  Files         393      393              
  Lines       27389    27392       +3     
  Branches     2027     2027              
==========================================
+ Hits        19681    19695      +14     
+ Misses       7140     7129      -11     
  Partials      568      568              

Impacted Files	Coverage Δ
src/ert/_c_wrappers/analysis/analysis_module.py	86.59% <ø> (+4.07%)	⬆️
...rc/ert/shared/models/iterated_ensemble_smoother.py	90.69% <100.00%> (+1.08%)	⬆️

... and 2 files with indirect coverage changes

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[dafeda]

I tried writing a GUI test as well, but it is made difficult by the fact that ERT produces different results even when RANDOM_SEED is set. See #5083 for details.

This will need to be solved before writing a GUI test for this. Here's an issue: #5084

[eivindjahren]

Should the RANDOM_SEED not be set in this run?

[eivindjahren]

Ah, I see that you are using append so that is the reason._

[eivindjahren]

🙏