### Elasticsearch Version

8.9.0

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

any

### Problem Description

If the context text supplied to the Question Answering task is longer than the model's `max_sequence_length` and `truncate` is set to `none` then inference on the model fails with the message:

```
status_exception: question answering result has invalid dimension, expected 2 found [6] 
```
<img width="1438" alt="Screenshot 2023-07-25 at 08 21 37" src="https://github.com/elastic/elasticsearch/assets/2353640/12d296f6-03b2-4cda-89ce-7399348c4104">


### Steps to Reproduce

Use long input text to the question answering task


### Work Aroundf
The fix is to truncate the context which unfortunately may remove the part of the document containing the answer. For reference the call is documented here

```
POST _ml/trained_models/distilbert-base-cased-distilled-squad/deployment/_infer
{
  "docs":[{ "text_field": "question answering context"}],
  "inference_config": {
    "question_answering": {
      "question": "The question to ask",
      "tokenization": {
        "bert": {
          "truncate": "second",
          "span": -1          
        }
      }
    }
  }
}
````

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/inference/nlp/tokenizers/TokenizationResult.java
List<Tokens> getTokens() {
        return tokens;
    }
    public String getFromVocab(int tokenId) {
        return vocab.get(tokenId);
    }
    public String decode(String token) {
        return token;
    }
    public Tokens getTokenization(int tokenizationIndex) {
        return tokens.get(tokenizationIndex);
    }
    public boolean anyTruncated() {
        return tokens.stream().anyMatch(Tokens::truncated);
    }
    public boolean isEmpty() {
        return this.tokens.isEmpty() || this.tokens.stream().allMatch(t -> t.tokenIds.length == 0);
    }
    public abstract NlpTask.Request buildRequest(String requestId, Tokenization.Truncate t) throws IOException;
    protected void writePaddedTokens(String fieldName, XContentBuilder builder) throws IOException {
        builder.startArray(fieldName);
        for (var inputTokens : tokens) {
            builder.startArray();
            
            for (int t : inputTokens.tokenIds) {
                builder.value(t);
            }
            for (int i = inputTokens.tokenIds.length; i < maxLength; i++) {
                builder.value(padTokenId);
            }