feat: Add Gemini Flash

[QuietRocket]

Description

I duplicated Gemini 1.5 Pro and renamed it to Gemini 1.5 Flash.

Fixes #4611

Type of Change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• [x] Ran docker compose middleware, Flask API, yarn dev frontend, and made a workflow with Gemini Flash. It works.