feat: support custom stages

[klkvr]

trafficstars

Based on #18955

Allows defining custom stages on NodeAddOns. Those stages are added to pipeline and advanced in PersistenceService.

Open questions:

• Is there a better place for the custom_stages getter? Maybe Node trait?
• How appropriate is it to advance stages directly in the PersistenceService? This should work fine for most of the cases, especially for custom indexes. Another approach would be allowing to define custom hooks invoked when persisting but it feels like this might just lead to redundancy in custom stage impls