test: improve fixture definition by constraining dataset IDs

[ireneisdoomed]

✨ Context

We use dbldatagen to build mock dataframes given a specific schema. We use this mock dataframes to test that the logic returns data in the correct format. For content testing, we have to manually define how we want the data to look like.

In a recent PR, there is one test that is failing because the tested logic involves joining different mock datasets. The join doesn't return any common rows, therefore the test fails.

This PR aims to make the automatically generated datasets more useful by adding a constraint in the ID fields of each dataset so that joins will be successful.
After this PR is merged, the failing test in the above mentioned PR will no longer fail.

🛠 What does this PR implement

• All main ID fields in each dataset will be between 1 and 400 (the number of rows we randomly generate)
• Other minor constraints like providing a list of all possible study types

🙈 Missing

🚦 Before submitting

• Do these changes cover one single feature (one change at a time)?
• Did you read the contributor guideline?
• Did you make sure to update the documentation with your changes?
• Did you make sure there is no commented out code in this PR?
• Did you follow conventional commits standards in PR title and commit messages?
• Did you make sure the branch is up-to-date with the dev branch?
• Did you write any new necessary tests?
• Did you make sure the changes pass local tests (make test)?
• Did you make sure the changes pass pre-commit rules (e.g poetry run pre-commit run --all-files)?

[project-defiant]

Care to say that this should be an enum (in the future)