The CloudWatch Agent sends PutMetricData with an empty top-level
MetricData and every datum nested under EntityMetricData[].MetricData.
Both the JSON 1.0 handler (also reached by Smithy RPC v2 CBOR) and the
Query handler read only the top-level list, so the agent's metrics were
silently dropped.
Both handlers now append each EntityMetricData entry's datums to the
top-level ones and store them under the request Namespace, with the same
parsing as top-level datums. Entity and StrictEntityValidation are
accepted and ignored. The per-request INFO logs of the raw request and
parsed datums are lowered to a DEBUG count.
Fixes#6066
(cherry picked from commit 03f57303969561b049c3ebba38f1fd9d2b68df4c)
Mohith