fix: respect sparkConf pod template settings when spec.template is nil

[Denyme24]

Purpose of this PR

fixes #2793

Proposed changes:

Modified driverPodTemplateOption() and executorPodTemplateOption() in submission.go to always generate pod template files, even when they are not explicitly provided by users.

Changes

• Removed the early return when app.Spec.Driver.Template == nil and app.Spec.Executor.Template == nil
• Create minimal default pod templates with a base container structure when user templates are not provided
• Ensure sparkConf pod template settings are properly applied via pod template files, even without explicit templates
• Always write pod template files to:
  • /tmp/spark/{submissionID}/driver-pod-template.yaml
  • /tmp/spark/{submissionID}/executor-pod-template.yaml

Result

This ensures that sparkConf settings relying on pod templates (e.g., resource limits, node selectors, etc.) are respected regardless of whether users define pod templates in their SparkApplication spec.

Change Category

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

Checklist

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

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[Denyme24]

hey team @nabuskey @ImpSy, PTAL.

[Denyme24]

hey @ChenYi015 @Shekharrajak, please review these changes.
thank you.