More resilient manifest application

[twz123]

Is your feature request related to a problem? Please describe.

The Manifest Deployer part of k0s could be more resilient and its performance relies on the current way in which components are initialized and run, even if it shouldn't matter.

• Sometimes new stacks are missed: First start watching bundle dir, then list/add existing dirs #1781
• fsnotify events trigger a stack application even if those files would be ignored by the applier later on: Refactor StackApplier #1815
• Files are written directly into the manifest folders, without any precautions that there might be files that are not fully written yet. This leads to situations where the stack applier behaves strangely (3845479): Write manifests atomically #1816

Describe the solution you would like

Refactor the code to iron out edge cases.

Describe alternatives you've considered

Leave it as is. Works 99% of the time. The 1% will be hard to debug.

Additional context

No response