embeddings compatibility for OpenAI [examples/server]

[wujjpp]

Add router for serve /v1/embeddings

1. input as string

curl http://127.0.0.1:8080/v1/embeddings \
    -H 'Content-Type: application/json' \
    -d '{
        "input": "hello",
        "model":"GPT-4",
        "encoding_format": "float"
    }'

response

{
    "data": [
        {
            "embedding": [
                -3.697190046310425,
                ...
                -4.443967342376709
            ],
            "index": 0,
            "object": "embedding"
        }
    ],
    "model": "GPT-4",
    "object": "list",
    "usage": {
        "prompt_tokens": 0,
        "total_tokens": 0
    }
}

2. input as string array

curl http://127.0.0.1:8080/v1/embeddings \
--header 'Content-Type: application/json' \
--data '{
        "input": ["hello","world"],
        "model":"GPT-4",
        "encoding_format": "float"
}'

response

{
    "data": [
        {
            "embedding": [
                -3.697190046310425,
                ...
                -4.443967342376709
            ],
            "index": 0,
            "object": "embedding"
        },
        {
            "embedding": [
                -0.35142484307289124,
                ...
                -4.626900672912598
            ],
            "index": 1,
            "object": "embedding"
        }
    ],
    "model": "GPT-4",
    "object": "list",
    "usage": {
        "prompt_tokens": 0,
        "total_tokens": 0
    }
}