Fetch doc images from ert-testdata

[berland]

These images are now stored in another repository

See also #13650

Issue
Resolves #13608

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.21%. Comparing base (1f514fc) to head (0581eb7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13650   +/-   ##
=======================================
  Coverage   89.21%   89.21%           
=======================================
  Files         469      469           
  Lines       33257    33257           
=======================================
  Hits        29670    29670           
  Misses       3587     3587           

Flag	Coverage Δ
cli-tests	35.53% <ø> (ø)
fuzz	43.71% <ø> (ø)
gui-tests	59.46% <ø> (-0.02%)	⬇️
performance-and-unit-tests	77.82% <ø> (ø)
test	45.09% <ø> (ø)

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