feat: FTRS-4392 updated processor to set skipped metric on no db changes

[lukasz-jercha-nhs]

Description

Updated metrics to increase skipped metric on no items found in the transaction bundle

Context

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[Copilot]

Pull request overview

Updates the data-migration service’s processing metrics so that “no-op” updates (where the DynamoDB transaction would be empty) are counted as skipped, and aligns unit + service-automation tests with the new metric behavior.

Changes:

• Increment metrics.skipped when there are no DynamoDB transaction items to write.
• Update service-automation Gherkin scenarios to expect skipped=1 for no-op updates.
• Update/add unit tests to validate the new skip-tracking behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/service_automation/tests/features/data_migration_features/incremental_updates/update_organisation_fields.feature	Adjusts expected SQS metrics for a no-op update to count as skipped.
tests/service_automation/tests/features/data_migration_features/incremental_updates/update_endpoints.feature	Adjusts expected SQS metrics for an endpoint no-change update to count as skipped.
tests/service_automation/tests/features/data_migration_features/incremental_updates/update_edge_cases.feature	Adjusts expected SQS metrics for multiple no-op update edge cases to count as skipped.
services/data-migration/tests/unit/service_migration/test_processor.py	Updates an existing metrics assertion and adds a unit test for empty-transaction skip tracking.
services/data-migration/src/service_migration/processor.py	Implements skip-metric increment when transaction_items is empty.