feat(js/plugins/google-genai): Support for veo-3.1-lite-generate-001

[ifielker]

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

[gemini-code-assist]

Code Review

This pull request adds the 'veo-3.1-lite-generate-001' model to the known models in the Vertex AI plugin and updates the 'veo-text-prompt' test application flow to utilize this new model. I have no feedback to provide.