Implement validation logic for `ScheduledSparkApplication` webhook

[puwun]

What feature you would like to be added?

Implement the empty validate() function in ScheduledSparkApplicationValidator

spark-operator/internal/webhook/scheduledsparkapplication_validator.go

Lines 91 to 94 in 85bda2e

	func (v *ScheduledSparkApplicationValidator) validate(_ *v1beta2.ScheduledSparkApplication) error {
	// TODO: implement validate logic
	return nil
	}

Why is this needed?

Invalid Schedule and TimeZone are currently caught in the controller, not the webhook. This means invalid resources are created and then marked as FailedValidation in status. Moving validation to webhook would reject invalid resources at creation time.

Describe the solution you would like

Move existing controller validation to webhook:

• Schedule: Cron syntax via cron.ParseStandard()
• TimeZone: time.LoadLocation() validation

Describe alternatives you have considered

Keep the current behaviour or remove validate() and its call sites entirely.

Additional context

No response

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[Raakshass]

Hi! I'd like to work on this issue. I've already implemented the validation logic for the ScheduledSparkApplication webhook in my local fork.

My implementation:

• Validates TimeZone using time.LoadLocation()
• Validates Schedule (cron expression) using cron.ParseStandard()
• Includes comprehensive unit tests

I'll submit a PR with signed commits once I've verified all tests pass. Thanks!