Azure Monitor input plugin does not watch for new resources

### Relevant telegraf.conf

```toml
[[inputs.azure_monitor.subscription_target]]
resource_type = "Microsoft.Compute/disks"
metrics = [
"Composite Disk Read Bytes/sec",
"Composite Disk Read Operations/sec",
"Composite Disk Write Bytes/sec",
"Composite Disk Write Operations/sec",
]
aggregations = [ "Average" ]
```

### Logs from Telegraf

```text
No valuable logs since the issue relates to new resources that are not identified/included by Telegraf after creation.
```

### System info

Commit d7f3a0e, Ubuntu 22.04, Kubernetes 1.29

### Docker

_No response_

### Steps to reproduce

1. Install and run telegraf monitoring Azure resources
2. Create a new resource for a type that is monitored by Telegraf (example used disk, so a PVC in k8s)
3. Check if metrics for the new resources are sent

### Expected behavior

New resources should be monitored by Telegraf without the need for a restart (which adds the new resource).

### Actual behavior

New resource is not monitored until restart.

### Additional info

There should be some kind of watch mechanism to include new resources.

Start by locating the Azure Monitor input plugin and its subscription_target resource discovery path. Reproduce the documented sequence by creating a monitored resource after Telegraf starts, then trace how resources are initially identified. Done means newly created resources are monitored without restarting Telegraf.

Written by the indexing model from the issue text.