[Feature Request]: Add support to gemini-embedding-exp-03-07

Self Checks

• I have searched for existing issues search for existing issues, including closed ones.
• I confirm that I am using English to submit this report (Language Policy).
• Non-english title submitions will be closed directly ( 非英文标题的提交将会被直接关闭 ) (Language Policy).
• Please do not modify this template :) and fill in all the required fields.

Is your feature request related to a problem?

No

Describe the feature you'd like

Add support to gemini-embedding-exp-03-07, which seems to be a promising embedding model, and currently does not appear in Gemini model list.

Describe implementation you've considered

No response

Documentation, adoption, use case

Additional information

https://developers.googleblog.com/en/gemini-embedding-text-model-now-available-gemini-api/
https://ai.google.dev/gemini-api/docs/models#gemini-embedding
Input token limit: 8,192
Output dimension size: Elastic, supports: 3072, 1536, or 768

The issue names the Gemini embedding model and links its Google documentation, but provides no repository files, tests, or implementation entry point. Start by reading the linked model documentation and comparing it with RAGFlow's current supported-model listing; done should include the model appearing there with the documented token limit and supported output dimensions.