Split startups per layer + fix default image manager path

[kbeaugrand]

Description

What's new?

• Fix Bug: Default Image stream is null #1644
• Resolve Feature: Split Startup configurations by layer #1543

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Tests
• Other

[codecov]

Codecov Report

Base: 90.13% // Head: 90.13% // No change to project coverage 👍

Coverage data is based on head (8766a31) compared to base (001194b).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1645   +/-   ##
=======================================
  Coverage   90.13%   90.13%           
=======================================
  Files         268      268           
  Lines        8840     8840           
=======================================
  Hits         7968     7968           
  Misses        872      872           

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