Roberta embedding

[maxdebayser]

This is a Draft PR based on PR #5447 to test Roberta embedding models.

To run cuda graphs have to be disabled because they aren't supported with encoder models

python -m vllm.entrypoints.openai.api_server --model /path/to/roberta --served-model-name roberta --enforce-eager

To test with the embeddings API:

curl http://localhost:8000/v1/embeddings \
  -H "Content-Type: application/json" \
  -d '{
    "input": "Your text string goes here",
    "model": "roberta"
  }'

[github-actions]

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[maxdebayser]

TODO: It's strange that just adding another head size here makes the code run. Perhaps this is actually a silent failure and the actual kernel has to be added somewhere.

[maxdebayser]

Closed in favor of #9387