fix(frontend): don't rename continuous covariate columns

[eatyourgreens]

The preview step renames columns like Dose, Age, or Weight to Cont Covariate. This causes problems since column names must be unique. Here, continuous covariate columns are not renamed before uploading to the backend.

[sonarcloud[bot]]

Quality Gate passed for 'pkpdapp'

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

[codecov[bot]]

Codecov Report

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

Project coverage is 76.86%. Comparing base (28944d1) to head (5f12f38). Report is 19 commits behind head on development.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #470 +/- ## =============================================== - Coverage 76.88% 76.86% -0.02% =============================================== Files 108 108 Lines 5593 5590 -3 =============================================== - Hits 4300 4297 -3 Misses 1293 1293 ```

:umbrella: View full report in Codecov by Sentry.
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[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