Support non-indexed sourced_from source types in data warehouse ingestion

[ellisandrews-toast]

Context

#1273 added support for pure-source types: types that feed sourced_from fields on other types without calling t.index (see #1342, #1343, #1346, #1347, #1356). Events for these types are validated and their sourced fields flow to the destination type's index, but the warehouse gems don't handle them.

Problem

Events for a non-indexed source type never reach the data warehouse:

1. No warehouse table is defined. Warehouse tables hang entirely off indices: every t.index automatically gets a table (FactoryExtension#new_index in elasticgraph-warehouse/lib/elastic_graph/warehouse/schema_definition/factory_extension.rb), the warehouse_table / exclude_from_warehouse customization API lives on the index object (index_extension.rb), WarehouseTable itself is Data.define(:name, :index), and ResultsExtension#generate_warehouse_config collects tables via each type's own_index_def. A type with no index has no table and no place to declare one.
2. No operation survives to be dumped. WarehouseDumper#build_jsonl_file_from treats the __self update target (where op.update_target.type == op.event.fetch("type")) as the event's "primary write" (elasticgraph-warehouse_lambda/lib/elastic_graph/warehouse_lambda/warehouse_dumper.rb:116). A non-indexed type has no __self update target — its events only produce operations targeting the destination type's index — so every operation is filtered out and no S3 file is written (the dumper skips empty groups).

Note that (2) isn't just a matter of relaxing the filter: no operation carries the full source-event payload (the sourced_from update targets' script params only contain the sourced field values, shaped for the destination document). Warehouse ingestion would need a representation of the raw source event itself.

The warehouse is arguably the one place raw source events should remain visible — the datastore only ever holds the copied fields — so silently dropping them seems wrong.

What's needed

• Generalize warehouse table generation to cover ingestible non-indexed types (the same "ingestible types" set used for the event envelope enum in Include non-indexed sourced_from source types in the event envelope type enum #1346, exposed as Results#sourced_update_targets_by_source_type_name). The column derivation should port cleanly — WarehouseTable#table_schema already builds from indexing_fields_by_name_in_index, which non-indexed types have — but the table needs to be keyed off the type rather than an index, and the warehouse_table / exclude_from_warehouse API needs a home for types without an index block.
• Give WarehouseDumper a primary-write signal (and a payload source) that doesn't depend on a __self update target.

Open question

Indexed types get a warehouse table automatically, with exclude_from_warehouse as the opt-out. Should pure-source types follow the same automatic-with-opt-out convention, or should their tables be explicit opt-in?