[Go] Gemini model capabilities differ between JS and Go

[olivoil]

Describe the bug

The model capabilities for Gemini models (flash and pro) differ between JS and Go.

In Go, in the google ai and vertex ai plugins, the systemRole capability is set to false.

In JS, it is set to true in google ai and vertex ai plugins.

To Reproduce

Use a dotprompt that contains a system message, for example this one that is in the go documentation.

---
model: vertexai/gemini-1.5-pro
input:
  schema:
    userQuestion: string
---

{{role "system"}}
You are a helpful AI assistant that really loves to talk about food. Try to work
food items into all of your conversations.
{{role "user"}}
{{userQuestion}}

Run this prompt using both JS and Go implementations. JS will work, but the Go implementation will return an error.

Expected behavior

This Dotprompt should work with both JS and Go implementations.

Runtime (please complete the following information):

• OS: MacOS
• Version: 14.5

** Go version

• go version go1.22.5 darwin/arm64