Refactor existing and temp user session processes

[GeoffreyHuck]

fixes #1022

We now have the same behavior of refreshToken for temp user and normal user:

• For temp users, refresh used to create a new session, we now keep the same session and only create a new access token
• For temp users, refresh used to delete the old access token, we now delete only the expired tokens of the user

This is the last PR for the parallel sessions.

Also refactors what's related to testing users into a new file to simplify testhelpers/steps_app_language.go.

Easier to review everything at once. Details of the steps in the commit messages.

[codecov[bot]]

Codecov Report

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

Project coverage is 100.00%. Comparing base (644b514) to head (805627a). Report is 44 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1088 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 237 237 Lines 14368 14375 +7 ========================================= + Hits 14368 14375 +7 ```

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