(fix)API: Correctly pass scheduled job proxy env vars when launching jobs

[mgonnav]

Description

• In the launch_job task called by scheduled jobs to launch jobs, we were not adding the env vars related to the proxy provider selected for the scheduled job.
• In this PR we:
  • Fix scheduled jobs not passing proxy env vars correctly to jobs
  • Refactor the logic to add the corresponding proxy provider env vars
  • Format code

Issue

• Issue ID

Checklist before requesting a review

• I have performed a self-review of my code.
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• I have made corresponding changes to the documentation.
• New and existing tests pass locally with my changes.
• If this change is a core feature, I have added thorough tests.
• If this change affects or depends on the behavior of other estela repositories, I have created pull requests with the relevant changes in the affected repositories. Please, refer to our official documentation.
• I understand that my pull request may be closed if it becomes obvious or I did not perform all of the steps above.

[joaquingx]

LGTM