[ModelRunner] Support embedding inputs

[Potabk]

What this PR does / why we need it?

• Adds support for passing prompt_embeds to LLM.generate as

llm.generate({"prompt_embeds": input_embeds}, sampling_params)

or

llm.generate(
    [{"prompt_embeds": input_embeds} for input_embeds in inputs_embeds], sampling_params
)

• Add prompt_embeds to examples

Does this PR introduce any user-facing change?

How was this patch tested?

CI passed with new added/existing test.
and I have test with the example script in this pr, and the output seems looks good:

[Single Inference Output]
------------------------------
The capital of France is Paris. Paris is the largest city in France and is
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Adding requests: 100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 3/3 [00:00<00:00, 3966.87it/s]
Processed prompts: 100%|█████████████████████████████████████████████████████████████████████████| 3/3 [00:00<00:00,  3.99it/s, est. speed input: 177.08 toks/s, output: 63.91 toks/s]

[Batch Inference Outputs]
------------------------------
Q1: Please tell me about the capital of France.
A1: The capital of France is Paris. It is located in the northern part of the

Q2: When is the day longest during the year?
A2: The day is longest during the year at the summer solstice. This typically occurs

Q3: Where is bigger, the moon or the sun?
A3: The sun is significantly bigger than the moon. 

The sun has a diameter of

------------------------------

[Potabk]

@wangxiyuan this is ready for review

[wangxiyuan]

it's good to add a test as well

[wangxiyuan]

Nice example