Feat/lab-test-data: Create test lab_df and health_insurance_df

[signekb]

This pr will include the following:

• [X] The addition of functions.R
• [X] The addition of create_test_lab_df() in functions.R
• [X] The addition of lab_df in create_test_data.R using the create_test_lab_df(). lab_df has 100 rows (1 row per individual)
• [ ] The addition of a create_test_health_insurance_df() function in functions.R
• [ ] The addition of health_insurance_df in in create_test_data.R using the create_test_health_insurance_df(). health_insurance_df has 100 rows (1 row per individual)

Is this somewhat what you meant in #4 under Lab data, @Aastedet? From the description, I'm not sure whether there should be multiple rows per individual?

[signekb]

Renamed this branch to include both lab and health insurance test data. Will create new pr as well.