[BUG] ML Model Registration endpoints fail due to parameter requirements check

[nathaliellenaa]

What is the bug?
ML Model Registration endpoints are failing due to a breaking change from the core. The current implementation allows optional path parameters (model_id and version) in endpoints like /_plugins/_ml/models/{model_id}/{version}/_register and /_plugins/_ml/models/_register. However, the core now requires all defined path parameters to be consumed, making the current optional parameter handling invalid (ref).

The check for the parameters was introduced in 1.0.0-alpha1 version, specifically in this commit.

How can one reproduce the bug?
Running this in dev tools:

POST /_plugins/_ml/models/xv-F5pMBrJdjeJHHBXXV/1.0.0/_register

Resulted in this error:

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "request [/_plugins/_ml/models/xv-F5pMBrJdjeJHHBXXV/1.0.0/_register] contains unrecognized parameters: [model_id], [version]"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "request [/_plugins/_ml/models/xv-F5pMBrJdjeJHHBXXV/1.0.0/_register] contains unrecognized parameters: [model_id], [version]"
  },
  "status": 400
}

What is the expected behavior?
All defined path parameters should be properly consumed by the REST handler. The registration request should be processed without throwing IllegalArgumentException about unrecognized parameters.