Function find_pruneable_entry_id_for_topic

pub(crate) async fn find_pruneable_entry_id_for_topic(
    table_metadata_manager: &TableMetadataManagerRef,
    leader_region_registry: &LeaderRegionRegistryRef,
    topic: &str,
) -> Result<Option<u64>>

Finds the prunable entry id for the topic.

Returns None if:

• The topic has no region.
• Some region info is missing from heartbeat.