Bugs in `populate investigations` command

[praffq]

Describe the bug

1. when running this command the groups are created again and again.
2. No many to many relationships are set up and the relationship table is empty.

To Reproduce Steps to reproduce the behavior:

1. run python manage.py populate_investigations
2. Go to database and see the entries in the facility_patientinvestigation_groups table, you'll find there are no entries
3. run the above command multiple times , facility_patientinvestigationgroups table will have duplicate values created

Expected behavior

1. many to many relationship table should have the valid data
2. No duplication of data