Nonlocal Datadog Agent Does not Get Properly Configured

#### Overview of the Issue

Currently, we have a telemetry config such as:

```hcl
telemetry = {
dogstatsd_addr = "EXTERNAL_DNS_NAME"
}
```

And it seems as though, the datadog cluster in envoy still gets configured as `127.0.0.1`:

```json
{
"name": "datadog_local",
"connect_timeout": "3s",
"dns_lookup_family": "V4_ONLY",
"load_assignment": {
"cluster_name": "datadog_local",
"endpoints": [
{
"lb_endpoints": [
{
"endpoint": {
"address": {
"socket_address": {
"address": "127.0.0.1",
"port_value": 8126
}
}
}
}
]
}
```

It seems the telemetry attribute is not respecting the external datadog configuration, and datadog is not getting consul or envoy metrics.

#### Reproduction Steps

Steps to reproduce this issue, eg:

1. Create an external datadog agent
1. start a consul agent with connect and an envoy sidecar, configuring telemetry `dogstatsd_addr` for the external datadog agent
1. Datadog will not receive metrics, and the envoy configuration will have the datadog cluster configured for 127.0.0.1.

### Consul info for both Client and Server

Consul 1.15.3

Consul 1.15.3

### Operating system and Environment details

AWS Fargate

Start by reproducing the telemetry configuration with dogstatsd_addr set to an external Datadog agent on Consul 1.15.3 with Connect and an Envoy sidecar. Trace how that setting produces the datadog_local Envoy cluster; done means the cluster uses the external address instead of 127.0.0.1 and Datadog receives Consul and Envoy metrics.

Written by the indexing model from the issue text.