Support the Migration of Team Calendar for Confluence

Issue Summary

Currently, Confluence Cloud Migration Assistant doesn't support the migration of Team Calendars and it would require the manual works:

• Export Team Calendars Content to Other Calendars
• Add other calendars - Import Calendar

Suggested Solution

• Support the export/import of Team Calendar data
• Provide the REST API to bulk export/create the calendars
• Ability to migrate Team Calendar data using Confluence Cloud Migration Assistant

Why this is important

• Team Calendar is one of our most used plugins and it could be hundreds or thousands of calendars created within the instance
• It's not feasible to manually export/import hundreds or thousands of calendars
• When we perform the migration from Server to Cloud, we are hoping to minimize the data loss after the migration.