Support Timestream for InfluxDB Endpoints in Telegraf Timestream Output Plugin

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### Use Case

The current Telegraf Timestream output plugin only supports the Timestream LiveAnalytics (Write API) endpoints.

However, AWS has deprecated/limited access to Timestream LiveAnalytics, and is now promoting Timestream for InfluxDB as the recommended ingestion path.

Ideally, the plugin would:

* detect and support the timestream-influxdb ingestion API
* allow configuration of the InfluxDB-compatible endpoints
* fall back gracefully when LiveAnalytics is unavailable

This would ensure Telegraf remains compatible with the current direction of Amazon Timestream and newer AWS regions.

### Expected behavior

Add support for the timestream-influxdb service endpoints exposed by AWS:

AWS CLI reference: https://docs.aws.amazon.com/cli/latest/reference/timestream-influxdb/

This would enable Telegraf users to write metrics into AWS Timestream even in regions where LiveAnalytics is not deployed or available to new customers.

### Actual behavior

In supported regions, accounts receive:

```
aws timestream-write describe-endpoints --region eu-central-1

An error occurred (AccessDeniedException) when calling the DescribeEndpoints operation:
Only existing Timestream for LiveAnalytics customers can access the service.
Reach out to AWS support, for more information.

```

Trying to use the plugin in regions where LiveAnalytics is not available leads to errors:

```
aws timestream-write describe-endpoints --region me-central-1

Could not connect to the endpoint URL: "https://ingest.timestream.me-central-1.amazonaws.com/"
```

The current implementation uses the AWS SDK’s Timestream Write client:
https://github.com/influxdata/telegraf/blob/467473bdb7087e42a5c1c11e63d64731883eb079/plugins/outputs/timestream/timestream.go#L17

### Additional info

Telegraf 1.36.4 (git: HEAD@467473bd)

Start in plugins/outputs/timestream/timestream.go, where the AWS SDK Timestream Write client is used, and compare its current endpoint flow with the AWS CLI timestream-influxdb reference. Done means the plugin can configure and use Timestream for InfluxDB endpoints and handles unavailable LiveAnalytics access gracefully.

Written by the indexing model from the issue text.