Issue #3003 : Add Output transform metrics transform

[mattcasters]

Port Kettle Output steps metrics as a Hop-native Output transform metrics transform.

Fixes #3003

What

A local-engine generator that waits for listed sibling transform copies to finish, then emits one metrics row per copy (name, plugin id, line counters, rejected rows, duration). Incoming hops are not consumed and are treated as an error because they can deadlock the pipeline.

Why

Pipeline Logging / Execution Information cover project-wide monitoring, but they do not replace this in-pipeline transform for Kettle/PDI migrations.

How

• New plugin plugins/transforms/transformsmetrics, plugin id TransformsMetrics (deprecated extra id StepsMetrics).
• Metadata is @HopMetadataProperty with Hop transform* XML keys. The dialog uses grouped GuiCompositeWidgets tabs plus a TableView extra group.
• Runtime follows BlockUntilTransformsFinish wait semantics, then emits metrics instead of passing rows through.
• Kettle import maps StepsMetrics → TransformsMetrics and step* tags → transform* (including the Kettle steplineswrittentfield typo). Stored output field values are left unchanged.

Tests

• Unit: XML round-trip, getFields, check() (TransformsMetricsMetaTest)
• Import: Kettle snippet rewrite (KettleImportTransformsMetricsTest)
• Integration: 0110-output-transform-metrics with a golden dataset

Docs

User-manual page, sample pipeline, Transforms and Fields tab screenshots.

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