Stabilize timeline aggregate as the new state_aggregate

[WireBaron]

Timeline aggregate

What evidence do we have the feature is being used

We do see some instances using this in our function telemetry, though this may be test instances.

Why do we feel this feature is ready to be stable

This aggregate is just a specialized form of a state aggregate, which is being stabilized now as well (#690).

Is there any known further work needed on this feature after stabilization

No

Are there any compatibility concerns that may arise during future work on this feature

No

Feature History

• Experimental release version: 1.13.0
• Last version modifying on-disk format: 1.13.0
• Target stabilization version: 1.14.0

Stabilization checklist:

• Ensure tests exist for all public API
• Ensure API documentation exists and is accurate
• Remove toolkit_experimental tags and update test usages
• Add arrow operators for accessors if applicable
• Ensure arrow operators have test coverage
• If present, ensure combine and rollup are tested
• Add serialization tests for text format
• Add serialization tests for on disk format
• Add upgrade tests
• Add continuous aggregate test
• Add feature level documentation

[WireBaron]

We've decided that timeline aggregate ended up as a far more useful form of the state_aggregate, encasing a superset of that aggregates functionality. For that reason we'll be renaming timeline_agg as the more understandable state_agg. The current state_agg will be renamed and left as experimental to determine if it has enough value to stabilize later.