### 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_
self,
        context: RequestContext,
        request: PutMetricAlarmInput,
    ) -> None:
        
        if not request.get("TreatMissingData", "missing") in [
            "breaching",
            "notBreaching",
            "ignore",
            "missing",
        ]:
            raise ValidationError(
                f"The value {request['TreatMissingData']} is not supported for TreatMissingData parameter. Supported values are [breaching, notBreaching, ignore, missing]."
            )
        
        if request.get("Period"):
            
            value = request.get("Period")
            if value not in (10, 30):
                if value % 60 != 0:
                    raise ValidationError("Period must be 10, 30 or a multiple of 60")
        if request.get("Statistic"):
            if not request.get("Statistic") in [
                "SampleCount",
                "Average",
                "Sum",
                "Minimum",
                "Maximum",
            ]: