(PTFE-2629) Add backend for scaleway

[matthiasL-scality]

Purpose

Add scaleway backend to runner-manager

[codecov]

Codecov Report

❌ Patch coverage is 87.22222% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.15%. Comparing base (c28657f) to head (a33e363).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
runner_manager/backend/scaleway.py	85.53%	23 Missing ⚠️

❌ Your patch status has failed because the patch coverage (27.22%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #706      +/-   ##
==========================================
+ Coverage   84.91%   85.15%   +0.24%     
==========================================
  Files          35       36       +1     
  Lines        1545     1725     +180     
==========================================
+ Hits         1312     1469     +157     
- Misses        233      256      +23     

Flag	Coverage Δ
api	59.13% <27.22%> (-3.72%)	⬇️
unit	69.15% <87.22%> (+2.10%)	⬆️

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[cmeron]

It looks clean !

Too bad it doesn't support Elastic Metal but as it's using a different API entrypoint, it's not that simple to add cleanly.
Let's add instances for now!