Set default item in a container

Sets the specified item as the default (removes default flag from all others).

Container access tiers:

• Blocked (use dedicated routers): flows, chat, pages, dataconnections, prompts, aisearchendpoints, aimodelendpoints, mcpservers, aitoolproviders
• Blocked (use /user/* endpoints): chatlog, feedback, usersettings, userfavorites, usernotifications, usernotificationpreferences, usertheme, datasourcelastaccessed, onedrivelastaccessed
• Admin-only: settings
• Read-all, write-admin: theme, translation, sharepoint-entitlements
• Server-only (no API access): teamsconversationreferences, humaninput