REKDAT-262: Upgrade to CKAN 2.11.4

[bzar]

• Change CKAN version
• Update dependencies
• Upgrade ckanext-pages and ckanext-harvest
• Migrate CKAN session secret handling
• Remove prerun.py and migrate to separate connection test
• Fix robot tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.67%. Comparing base (450e75f) to head (86bf317).
⚠️ Report is 28 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #735      +/-   ##
==========================================
- Coverage   82.71%   82.67%   -0.05%     
==========================================
  Files          20       20              
  Lines        1950     1945       -5     
  Branches        1        1              
==========================================
- Hits         1613     1608       -5     
  Misses        337      337              

Flag	Coverage Δ
cdk	100.00% <ø> (ø)

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[Zharktas]

Ckan should not be installed in requirements.