Create 2.x branch for change to Google Vertex AI

Problem/Motivation

Google has announced that it's dropping its Google JSON API at the end of 2024 and will replace it with their new Google Vertex AI API.

• https://cloud.google.com/generative-ai-app-builder/docs/migrate-from-cse
• https://cloud.google.com/generative-ai-app-builder/docs/preview-search-r...
• https://cloud.google.com/sdk/docs/install

Proposed resolution

Build a new 2.x branch that supports the new AI, and has a migration process built in.

Remaining tasks

1. Learn how the new API works
2. Create new branch in project for changes
3. Update code to use new AI
4. Make adjustments to Admin interface
5. Create migration path from old system to new system

User interface changes

Admin interface will change, frontend should remain the same.

Data model changes

We need to support the new data required by the Vertex API to be able to make requests.