Add CoordinateSystem to ErtboxParameters

[frode-aarstad]

Issue
Resolves #12815

Approach
Short description of the approach

(Screenshot of new behavior in GUI if applicable)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Add backport label to latest release (format: 'backport release-branch-name')

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.65%. Comparing base (c999892) to head (f898b24).
⚠️ Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ert/analysis/_es_update.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12854      +/-   ##
==========================================
- Coverage   90.66%   90.65%   -0.01%     
==========================================
  Files         440      440              
  Lines       30513    30477      -36     
==========================================
- Hits        27664    27630      -34     
+ Misses       2849     2847       -2     

Flag	Coverage Δ
cli-tests	37.28% <83.33%> (-0.08%)	⬇️
gui-tests	67.89% <75.00%> (-0.42%)	⬇️
performance-and-unit-tests	77.07% <75.00%> (-0.04%)	⬇️
test	37.34% <50.00%> (-0.07%)	⬇️

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[codspeed-hq]

Merging this PR will not alter performance

✅ 34 untouched benchmarks

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_{Comparing frode-aarstad:ertbox-left-handed (f898b24) with main (0969869)}

[xjules]

Very good @frode-aarstad ! I think though this requires a storage migration.