Support for datastreams

### 🔖 Feature description
There is only a feature to give `indexPrefix` in the command line arguments and not an `index` or `datastream` itself.

### 🎤 Why is this feature needed ?
Given the advent of datastreams in the Elastic community, this feature would help folks generate logs and ingest it in a datastream post which they can test the behaviour of datastreams in various scenarios.

### ✌️ How do you aim to achieve this?
I am really not sure what I can do from my end. Maybe just allow an optional argument to pass explicit `indexName` or `datastream`

### 🔄️ Additional Information
Not applicable

### 👀 Have you spent some time to check if this feature request has been raised before?
I checked and didn't find similar issue

### Are you willing to submit PR?
Not really sure