Add optimization algorithms section in the documentation for the theory chapter

[roliveira]

This section includes the description and main differences between conmin_mfd and optpp_q_newton, both available through Dakota. The section was also cross-referenced in the backend section.

Credit goes to @olwijn for initially developing the document.

Issue
Resolves #9697

Approach
Added optimization_algorithms.rst section, updated the index.rst to include below the Theory chapter, and cross-referenced it from within the optimization_backend.rst section.

• 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 'pytest tests/ert/unit_tests -n logical -m "not integration_test"')

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: Create Backport PR to latest release

[codspeed-hq]

CodSpeed Performance Report

Merging #9698 will not alter performance

_{Comparing roliveira:9697-adding-section-on-constrainted-optimization-algorithms (2bbae26) with main (94439f5)}

Summary

✅ 24 untouched benchmarks

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.74%. Comparing base (3b745a6) to head (93326ea).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9698      +/-   ##
==========================================
+ Coverage   91.71%   91.74%   +0.02%     
==========================================
  Files         426      426              
  Lines       26538    26538              
==========================================
+ Hits        24340    24346       +6     
+ Misses       2198     2192       -6     

Flag	Coverage Δ
cli-tests	39.65% <ø> (ø)
everest-models-test	34.15% <ø> (-0.01%)	⬇️
gui-tests	74.32% <ø> (ø)
integration-test	37.99% <ø> (+<0.01%)	⬆️
performance-tests	51.58% <ø> (-0.01%)	⬇️
test	39.52% <ø> (+<0.01%)	⬆️
unit-tests	74.24% <ø> (+0.02%)	⬆️

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[roliveira]

Thanks for picking this up, I have now added the suggestions above.