Migration
There is no direct migration supported. After migrating your Server/Data Center to Confluence Cloud, you need to install Team Files for Confluence Cloud and connect folders again.
Feature Difference
Team Files for Confluence Cloud includes:
All the features available for Data Center and Server
Allowed Spaces ADMIN
Allowed users and groups ADMIN
Learn more about feature parity between Cloud and Data Center versions here:
Comparing Team Files for Confluence Cloud and Data Center