chore: change webhook payload structure

[bthari]

Summary

Changing the structure of the payload send from Turing to a webhook call, so we have the same structure across Merlin and Turing. From

{
    "event_type": "on-model-endpoint-created",
    "data": {} // the data being either ensembler/router/router_version 
}

to

{
    "event_type": "on-model-endpoint-created",
    "data": {
        "ensembler": {}, // omit if empty
        "router": {}, // omit if empty
        "router_version": {} // omit if empty
    }
}

I make the payload with this structure in case in the future we want to put several object in the payload (instead of just one object like now). I’m open to any advice if you have other opinions

[deadlycoconuts]

Ah oops I didn't know you needed it to be in exactly the same schema as the request body in Merlin, my bad. Thanks for fixing this!

[bthari]

No worries @deadlycoconuts! It's minor and simply for consistency matter, so user will not be confused why we have different schema, and I also just remember it this morning. Thank you for the quick review!