Ability to resume workflow when codecov push fails

[AlexVCaron]

Quick description

Codecov is not super stable right now. When the coverage upload fails, we need to re-run the whole test suite (long). This PR splits the workflow in twain, so only the second job fails when codecov push fails. Then, to retry the upload, re-run the workflow, specifying to run ONLY the failed jobs. Voilà ?

Type of change

Check the relevant options.

• [x] New feature (non-breaking change which adds functionality)

Checklist

• [x] My code follows the style guidelines of this project (run autopep8)
• [x] I added relevant citations to scripts, modules and functions docstrings and descriptions
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I moved all functions from the script file (except the argparser and main) to scilpy modules
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[codecov[bot]]

Codecov Report

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

Comparison is base (1c4b850) 65.92% compared to head (747da90) 68.12%. Report is 13 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #909 +/- ## ========================================== + Coverage 65.92% 68.12% +2.20% ========================================== Files 386 386 Lines 21573 20678 -895 Branches 3540 3160 -380 ========================================== - Hits 14222 14087 -135 + Misses 5720 5326 -394 + Partials 1631 1265 -366 ``` | [Components](https://app.codecov.io/gh/scilus/scilpy/pull/909/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | Coverage Δ | | |---|---|---| | [Scripts](https://app.codecov.io/gh/scilus/scilpy/pull/909/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `70.68% <ø> (+3.40%)` | :arrow_up: | | [Library](https://app.codecov.io/gh/scilus/scilpy/pull/909/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scilus) | `63.76% <ø> (+0.29%)` | :arrow_up: |