### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

PutMetricData with arrays of values does not work properly. Zero values seem to be published. PutMetricData with a single value works as expected. This happens to both CLI and SDK.

### Expected Behavior

PutMetricData with arrays of values should work as publishing a single value.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack:1.2.0

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)
```
awslocal cloudwatch put-metric-data --namespace test --metric-data MetricName=TestCounter,Values=10,1,Counts=1,1
awslocal cloudwatch get-metric-statistics --namespace test --metric-name TestCounter --statistics Maximum --period 60 --start-time 2022-11-9T00:00:00Z --end-time 2022-11-11T00:00:00Z
{
    "Label": "TestCounter",
    "Datapoints": [
        {
            "Timestamp": "2022-11-09T23:25:10+00:00",
            "Maximum": 0.0,
            "ExtendedStatistics": {}
        },
        {
            "Timestamp": "2022-11-09T23:27:10+00:00",
            "Maximum": 0.0,
            "ExtendedStatistics": {}
        }
    ]
}
```



### Environment

```markdown
- OS: Mac Monterey
- LocalStack: 1.2.0
```


### Anything else?

_No response_
region = aws_stack.extract_region_from_auth_header(request.headers)
        account_id = (
            extract_access_key_id_from_auth_header(request.headers) or DEFAULT_AWS_ACCOUNT_ID
        )
        backend = cloudwatch_backends[account_id][region]
        if backend:
            result = backend.metric_data
        else:
            result = []
        result = [
            {
                "ns": r.namespace,
                "n": r.name,
                "v": r.value,
                "t": r.timestamp,
                "d": [{"n": d.name, "v": d.value} for d in r.dimensions],
            }
            for r in result
        ]
        return {"metrics": result}
    def list_tags_for_resource(
        self, context: RequestContext, resource_arn: AmazonResourceName
    ) -> ListTagsForResourceOutput:
        tags = self.tags.list_tags_for_resource(resource_arn)
        return ListTagsForResourceOutput(Tags=tags.get("Tags", []))
    def untag_resource(