chore: merge sync & full-sync events

[karlkfi]

• Simplify the event handler by checking if full-sync is needed inside reconciler.Reconcile, based on the lastFullSyncTime.

Dependencies:

• https://github.com/GoogleContainerTools/kpt-config-sync/pull/1461
• https://github.com/GoogleContainerTools/kpt-config-sync/pull/1480
• https://github.com/GoogleContainerTools/kpt-config-sync/pull/1494
• https://github.com/GoogleContainerTools/kpt-config-sync/pull/1495

[google-oss-prow[bot]]

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