Add designmatrix for design2params

[larsevj]

Issue Resolves

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 'pytest tests/unit_tests -n logical -m "not integration_test"')

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

[larsevj]

Some remaining questions/issues from this pr:

• Need to figure out how we want to handle already existing gen_kw parameters, with the same name when creating an experiment from the design matrix. Design2params seems to prefer the already existent parameters in parameters.txt and drops the values from the designmatrix in this case. Note that design2params has no notion of parameter groups and so it will not necessarily detect duplicate param names, which will then be handled by design_kw.
• Design2params also produces designmatrix.txt and designparameters.txt in the runpath.
• Discuss how to combine initialization of parameters from design matrix and current run models.
• Add more validation and tests. For instance what happens if you input dates, or other types. Currently everything is parsed as strings and then converted to floats if possible.

[xjules]

@larsevj as discussed yesterday, let's split this PR into smaller ones; ie. I'd start by introducing DESIGN_MATRIX keyword.