added consistency in embed model names

[bhakarboy01]

Description of the change

added consistency for model names in embed_content function

Now, genai.embed_content function doesn't require a prefix of models/

Can be directly used as genai.embed_content( model="embedding-001", content="What is the meaning of life?", task_type="retrieval_document", title="Embedding of single string")

Motivation

Fixed consistency issue #466

Type of change

Feature request

Checklist

• [ ] I have performed a self-review of my code.
• [ ] I have added detailed comments to my code where applicable.
• [ ] I have verified that my change does not break existing code.
• [ ] My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• [ ] I am familiar with the Google Style Guide for the language I have coded in.
• [ ] I have read through the Contributing Guide and signed the Contributor License Agreement.

[bhakarboy01]

@MarkDaoust Please review this PR