fix(etl): count documents, not rows, in joining_props

[grzelaka-roche]

A joining index is read at its intermediate step, before its own translate_final flattens it to one row per document, so a document linked to several parents is still one row per link at that point. fn: count counted those rows

Count over the key of the joining index instead, and deduplicate the projection on that key so list and sum also see each document once. Both are skipped when the frame does not carry that key, falling back to the previous row count rather than silently merging distinct documents.

Also in the same path:

• drop the re-join of a key-only frame onto the aggregates, which multiplied every row of the joined index by its document count
• a group with no matching document now reads 0 instead of null. This is visible in Elasticsearch: guppy sees 0 where the field used to be missing
• build the aggregation expressions from the props that were actually projected, so a joining_props block mixing props with and without fn no longer builds agg(None)

Link to JIRA ticket if there is one:

New Features

Breaking Changes

Bug Fixes

• "count" aggregation in joining props now counts actual documents, not just rows and doesn't put "null" but 0 when there is no documents to count

Improvements

Dependency updates

Deployment changes