chore: Refactor to implement model plugin - part 4

[Fei-Guo]

This PR largely refactor the workspace spec validation code.

• Use information from registered model (remove PresetRequirementsMap) to do validation.
• The UTs for validation need to be rewritten. Comment all for now.
• Move interface definition to a separate directory to avoid cyclic import.
• Adjust to add

        GPUCountRequirement       string
	TotalGPUMemoryRequirement string
	PerGPUMemoryRequirement   string

to inference parameters.

[codecov]

Codecov Report

Attention: 25 lines in your changes are missing coverage. Please review.

Comparison is base (e0f3a35) 77.89% compared to head (490c6d6) 62.44%.

Files	Patch %	Lines
api/v1alpha1/workspace_validation.go	0.00%	20 Missing ⚠️
pkg/controllers/workspace_controller.go	20.00%	4 Missing ⚠️
api/v1alpha1/sku_config.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #190       +/-   ##
===========================================
- Coverage   77.89%   62.44%   -15.46%     
===========================================
  Files           9       14        +5     
  Lines        1095     1366      +271     
===========================================
  Hits          853      853               
- Misses        208      479      +271     
  Partials       34       34               

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