[ML] Cannot create inference endpoint with id `.elser_model_2` due to validation error

Elasticsearch Version

8.13

Installed Plugins

No response

Java Version

bundled

OS Version

any

Problem Description

Creating an inference endpoint with an id starting with . causes the validation failure

action_request_validation_exception: Validation Failed: 1: Invalid inference_id; '.elser_model_2' can contain lowercase alphanumeric (a-z and 0-9), hyphens or underscores; must start and end with alphanumeric;

Given that the ELSER model id is .elser_model_2 it is reasonable that someone would want to use the same id.

Steps to Reproduce

PUT _inference/sparse_embedding/.elser_model_2
{
  "service": "elser",
  "service_settings": {
    "num_allocations": 1,
    "num_threads": 1
  }
}

Logs (if relevant)