mcp: make autostart opt in for this release (microsoft#258713)

We might make it default in the future...

Author: connor4312

src/vs/workbench/contrib/chat/browser/chat.contribution.ts

@@ -303,7 +303,7 @@ configurationRegistry.registerConfiguration({
 		[mcpAutoStartConfig]: {
 			type: 'string',
 			description: nls.localize('chat.mcp.autostart', "Controls whether MCP servers should be automatically started when the chat messages are submitted."),
-			default: McpAutoStartValue.NewAndOutdated,
+			default: McpAutoStartValue.Never,
 			enum: [
 				McpAutoStartValue.Never,
 				McpAutoStartValue.OnlyNew,