refactor(backend): allow for multiple subject protocols

[eatyourgreens]

Link subjects to protocols via group.protocols, not subject.protocol. Change the Dataset model to group dosing rows by GROUP_ID, rather than SUBJECT_ID. Generate protocols and doses for rows that have AMOUNT_VARIABLE defined, so that each protocol is linked to a dosing compartment in the model.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.41%. Comparing base (95c077c) to head (ae3f641).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #492 +/- ## =============================================== - Coverage 76.76% 76.41% -0.35% =============================================== Files 108 108 Lines 5608 5606 -2 =============================================== - Hits 4305 4284 -21 - Misses 1303 1322 +19 ```

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[sonarcloud[bot]]

Quality Gate passed for 'pkpdapp'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
93.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarcloud[bot]]

Quality Gate passed for 'pkpdapp-team_pkpdapp_frontend'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud