fix(aws-dynamodb): paginate Query to avoid undercounting large result sets

[vidigoat]

Description

The AWS DynamoDB scaler's GetQueryMetrics issued a single dynamodb.Query call and returned that response's Count:

res, err := s.dbClient.Query(ctx, &dimensions)
...
return float64(res.Count), nil

A DynamoDB Query returns at most 1 MB of data per call and the result set can span multiple pages, signalled by a non-nil LastEvaluatedKey on the response. Because the scaler never followed that token, for any query whose matching items exceed a single page it only counted the first page and reported a Count far lower than the real number of matching items. This undercounts the metric and causes the workload to be under-scaled (the more items match, the worse the gap).

This is the same pagination pattern the AWS DynamoDB Streams scaler already uses (LastEvaluatedShardId).

Fix

Use dynamodb.NewQueryPaginator (which accepts the existing dynamodb.QueryAPIClient) to walk every page via LastEvaluatedKey and sum Count across all pages. Single-page results are unaffected, so this is non-breaking.

Tests

Added TestDynamoGetQueryMetricsPaginated: the mock returns two pages (4 items with a LastEvaluatedKey, then 3 items). It fails before the fix (returns 4) and passes after (returns 7). All existing DynamoDB scaler tests continue to pass.

Checklist

• Tests have been added
• Changelog has been updated and is aligned with our changelog requirements
• Commits are signed with Developer Certificate of Origin (DCO)

Fixes #

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