[WIP][Not Ready for Review]Pre-req work for SegmentAssignmentStrategy (#8585)

[GSharayu]

Currently, we have SegmentAssignment interface and OfflineSegmentAssignment & RealtimeSegmentAssignment as its implementation. This approach doesn't allow us to pick the custom segment assignment strategy.

This PR provides SegmentAssignmentStrategy as an interface improvement and pre-requisite work.

Issue #8585

[GSharayu]

@snleee @sajjad-moradi

[snleee]

Current code is moving SegmentAssignment to SegmentAssignmentStrategy. Instead, we would like to separate out the logic for SegmentAssignmentStrategy from SegmentAssignment. Ideally, I think that the following structure is needed:

1. SegmentAssignementStrategy -> ReplicaGroupSegmentAssignmentStrategy, BalancedSegmentAssignmentStrategy, CostBasedSegmentAssignmentStrategy etc
2. SegmentAssignment -> OfflineSegmentAssignment, RealtimeSegmentAssignment, etc

Offline/RealtimeSegmentAssignment implementation should pick replica group vs balanced based or other assignment strategy implementation on the table config.

Current code requires the code modification directly to OfflineSegmentAssignement or RealtimeSegmentAssignment if we want to add a new type of assignment strategy. The goal should be making that pluggable.

[jackjlli]

I also feed that the current offline/realtime segment assignment classes should extend from the same abstract base class, and inside that base class different assignment strategy can be chosen.

[jackjlli]

sed 's/SegmentAssignmentFactory/SegmentAssignmentStrategyFactory/'

[siddharthteotia]

This does not seem correct to me

OfflineSegmentAssignment or RealtimeSegmentAssignment is not a strategy imo

Regardless of offline v/s realtime, replica group and balanced are the concrete implementations of strategies

cc @jasperjiaguo since you are also going to touch related code later

[Jackie-Jiang]

I don't see the difference of the new SegmentAssignmentStrategy and the existing SegmentAssignment. If you want to plug-in custom assignment, just add the support to SegmentAssignmentFactory