[SUPPORT] DataDog Metrics Reporter using outdated DataDog API endpoint

**Describe the problem you faced**

I'm trying to configure `DataDogMetricsReporter` for many `DeltaStreamer` jobs and getting the following issue when using the `0.13.0` documentation for metrics (https://hudi.apache.org/docs/metrics/#datadogmetricsreporter):
```
Caused by: javax.net.ssl.SSLPeerUnverifiedException: Host name 'app.us.datadoghq.com'
does not match the certificate subject provided by
the peer (CN=*.datadoghq.com, O="Datadog, Inc.", L=New York, ST=New York, C=US)
```

**To Reproduce**

Steps to reproduce the behavior:

1. Follow Metrics documentation for DataDogMetricsReporter
2. Add API Key and turn metrics on
3. Deploy delta streamer job with the appropriate properties

**Expected behavior**

I expected to see the `hoodie.` prefixed metrics in DataDog.

**Environment Description**

* Hudi version : 0.13.0

* Spark version : 3.1

* Hive version : 2.3.1

* Hadoop version : 2.10.1

* Storage (HDFS/S3/GCS..) : S3

* Running on Docker? (yes/no) : No

**Additional context**

I've reached out to DataDog Support and they seem to say something similar regarding the outdated endpoint being the possible cause of this failure to write metrics to DataDog.

The Metrics Writer uses ["app.us.datadoghq"](https://github.com/apache/hudi/blob/master/hudi-client/hudi-client-common/src/main/java/org/apache/hudi/metrics/datadog/DatadogHttpClient.java#L51)
but the official documentation says the API needs to be [api.datadoghq.com](https://docs.datadoghq.com/api/latest/metrics/#submit-metrics).

Start in hudi-client/hudi-client-common/src/main/java/org/apache/hudi/metrics/datadog/DatadogHttpClient.java at the endpoint referenced on line 51, then compare it with DataDog's current metrics API documentation. Reproduce the DeltaStreamer configuration from the issue and verify that hoodie.-prefixed metrics reach DataDog successfully using the supported endpoint.

Written by the indexing model from the issue text.