refactor: Simplify cron scaler code

[joelsmith]

The current cron scaler code creates a cron object and starts it (which creates a goroutine and a lot of data to manage a cron engine) just so that it can find the next activation time. It also re-parses the cron strings on each iteration. This update only parses on creation of the trigger, then uses the cron schedule object directly to get the next activation time.

Checklist

• I have verified that my change is according to the deprecations & breaking changes policy
• Changelog has been updated and is aligned with our changelog requirements
• Commits are signed with Developer Certificate of Origin (DCO - learn more)

[JorTurFer]

/run-e2e cron
Update: You can check the progress here

[JorTurFer]

and now DCO xD

[SpiritZhou]

@joelsmith Do you mind also refactoring it with the new declarative scaler configuration? #5797

[rickbrouwer]

@joelsmith Do you mind also refactoring it with the new declarative scaler configuration? #5797

I have refactored it in #6098

[stale]

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