Update Vertex AI extension to provider workspace configuration changes

[jeffmaury]

Is your feature request related to a problem? Please describe

Move away from core

Describe the solution you'd like

See #2245 for the details of the configuration

Describe alternatives you've considered

No response

Additional context

No response

[coderabbitai]

🔗 Related PRs

#1671 - feat(vertex-ai): add Vertex AI extension for Anthropic models [merged]
#1714 - feat(guided-setup): wire Vertex AI panel to extension for onboarding [merged]
#1877 - fix(agent-workspaces): inject Vertex AI config into workspace at creation time [merged]
#2074 - feat(vertex-ai): persist connection IDs in workspace configuration [merged]

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