fix: datadog metric provider should use v2 endpoint

[alexef]

Summary

Datadog is moving away from the legacy v1 api to the GA v2 one. Rollouts metric provider should also follow this api change.

Note that the payload is slightly different, and the query is now part of attributes.queries.*.

Use Cases

Datadog imposes stricter limits on v1 vs v2 endpoints. This change will mitigate the 429 one may receive when running multiple AnalysisRuns with datadog as the metric source.