POC: Add design_matrix to ert

[oyvindeide]

Issue Will mean that users no longer need to comment in and out GEN_KW when doing sensitivity, simplifying their workflow. For now it is a new method of creating an ensemble, the user must then do Evaluate ensemble afterwards.

• [ ] 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 tests pass locally (after every commit!)

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

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 20.31250% with 102 lines in your changes missing coverage. Please review.

Project coverage is 85.68%. Comparing base (3aa9c85) to head (6e5db81). Report is 1 commits behind head on main.

Files	Patch %	Lines
.../ert/gui/tools/manage_experiments/design_matrix.py	12.98%	67 Missing :warning:
.../manage_experiments/ensemble_init_configuration.py	25.00%	33 Missing :warning:
src/ert/config/gen_kw_config.py	50.00%	1 Missing :warning:
src/ert/enkf_main.py	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #8099 +/- ## ========================================== - Coverage 86.03% 85.68% -0.35% ========================================== Files 382 383 +1 Lines 23706 23832 +126 Branches 622 634 +12 ========================================== + Hits 20395 20421 +26 - Misses 3236 3337 +101 + Partials 75 74 -1 ```

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