Store observations

[oyvindeide]

Issue
Resolves #my_issue

Approach
Short description of the approach

(Screenshot of new behavior in GUI if applicable)

Pre review checklist

• Read through the code changes carefully after finishing work
• Make sure tests pass locally (after every commit!)
• Prepare changes in small commits for more convenient review (optional)
• PR title captures the intent of the changes, and is fitting for release notes.
• Updated documentation
• Ensured that unit tests are added for all new behavior (See
  Ground Rules),
  and changes to existing code have good test coverage.

Pre merge checklist

• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.

[codecov-commenter]

Codecov Report

Merging #6302 (797b37a) into main (d57d133) will increase coverage by 0.00%.
The diff coverage is 97.95%.

@@           Coverage Diff           @@
##             main    #6302   +/-   ##
=======================================
  Coverage   83.80%   83.81%           
=======================================
  Files         342      343    +1     
  Lines       20759    20796   +37     
  Branches      862      862           
=======================================
+ Hits        17398    17430   +32     
- Misses       3062     3067    +5     
  Partials      299      299           

Files	Coverage Δ
src/ert/analysis/__init__.py	100.00% <ø> (ø)
src/ert/cli/main.py	92.75% <ø> (ø)
src/ert/config/observation_vector.py	92.68% <100.00%> (+0.37%)	⬆️
src/ert/config/observations.py	94.62% <100.00%> (-0.29%)	⬇️
src/ert/dark_storage/common.py	88.52% <100.00%> (ø)
src/ert/data/_measured_data.py	77.00% <100.00%> (-1.58%)	⬇️
src/ert/gui/ertwidgets/caselist.py	96.96% <ø> (ø)
src/ert/gui/simulation/simulation_panel.py	96.55% <ø> (ø)
src/ert/libres_facade.py	89.25% <100.00%> (+0.24%)	⬆️
src/ert/run_models/iterated_ensemble_smoother.py	94.93% <100.00%> (-0.07%)	⬇️
... and 6 more

... and 1 file with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[sondreso]

LGTM!