feat(tools): Add GoogleManagedMcpToolset for simplified Google MCP auth

[yugborana]

Introduces GoogleManagedMcpToolset, a McpToolset subclass that automates ADC-based authentication and endpoint URL resolution for Google Managed MCP servers (e.g., BigQuery).

• Auto-refreshes OAuth2 tokens via google.auth on every request
• Maps product names to endpoint URLs (initially supports 'bigquery')
• Supports custom scopes and project ID overrides
• Updates bigquery_mcp sample to use the new simplified API
• Adds 16 unit tests covering init, auth, and parameter forwarding

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Link to Issue or Description of Change

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• Closes: Create a subclass of MCPToolset to simplify connections to Google Managed MCP servers #3897
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[yugborana]

@GWeale @wuliang229 @ankursharmas @sasha-gitg