Refactor embedding model name in call

[Surya2k1]

Description of the change

Embedding model requires to mention as "models/<model_name>" but not other generative models which is simply "<model_name>"

Motivation

It just for consistency of model usage. May fix #640.

Type of change

Feature request

Checklist

• I have performed a self-review of my code.
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• I have verified that my change does not break existing code.
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