Generalize export obs tool

[SAKavli]

Issue
Resolves #13726

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 83.64198% with 53 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@ea9f05f). Learn more about missing BASE report.
⚠️ Report is 20 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/ert/gather_obs/summary_key_data.py	52.83%	25 Missing ⚠️
src/ert/gather_obs/gather_observations.py	83.80%	23 Missing ⚠️
src/ert/__main__.py	33.33%	2 Missing ⚠️
..._obs/observation_exporters/bulk_config_exporter.py	97.87%	2 Missing ⚠️
...t/gather_obs/observation_exporters/csv_exporter.py	95.23%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13746   +/-   ##
=======================================
  Coverage        ?   90.38%           
=======================================
  Files           ?      472           
  Lines           ?    33453           
  Branches        ?        0           
=======================================
  Hits            ?    30235           
  Misses          ?     3218           
  Partials        ?        0           

Flag	Coverage Δ
cli-tests	35.97% <73.45%> (?)
fuzz	43.55% <30.55%> (?)
gui-tests	59.19% <30.55%> (?)
performance-and-unit-tests	77.92% <62.65%> (?)
test	46.60% <0.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...observation_exporters/base_observation_exporter.py	100.00% <100.00%> (ø)
...t/gather_obs/observation_exporters/csv_exporter.py	95.23% <95.23%> (ø)
src/ert/__main__.py	85.66% <33.33%> (ø)
..._obs/observation_exporters/bulk_config_exporter.py	97.87% <97.87%> (ø)
src/ert/gather_obs/gather_observations.py	83.80% <83.80%> (ø)
src/ert/gather_obs/summary_key_data.py	52.83% <52.83%> (ø)

[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks

---

_{Comparing SAKavli:generalize-export-obs-tool (61a941a) with main (321dad2)}