Ingest V2 misses commit wait_for

[rdettai]

Is your feature request related to a problem? Please describe.
Similar to #4438 that tracks the behavior of CommitType::Force in ingest V2, this issue is about CommitType::wait in ingest V2. See the docs for the specs.

Describe the solution you'd like
Ingest V2 should behave like ingest V1 when using ?commit=wait_for

Describe alternatives you've considered
Remove the feature for ingest V2.

Additional context
With ingest V1, indexing was happening on the same node as the one receiving the query. This is not true anymore with ingest V2, so the notification system that makes the waiting possible should happen at the cluster level. Possible solutions:

• track commit progress and push notifications from the control plane
• communicate back the commits directly from the indexer to the original ingester

[rdettai]

#4438 (comment)

[rdettai]

this will be done as part of #5350 as commit=force also requires to wait