Add instructions to use Google and Google Cloud remote MCP servers

[fatoboist]

Describe the bug

Since remote Google MCP servers are in public preview, it would make sense to add instructions for using remote MCP servers in adk, perhaps using one of the products listed in https://docs.cloud.google.com/mcp/supported-products

Additional context

This is a feature request for GA of the remote MCP servers. See b/469436240