GRANT DROP ON TABLE springbootdb.* TO AdminUser
There isn't a specific "drop table" permission. But you can give them control on the schema using:

GRANT CONTROL ON SCHEMA::springbootdb TO AdminUser;


This allows them to drop any table in that schema, but also to do all kinds of other things you might not intend. You can take some of those things away with more granular DENY permissions, or with reactionary tools like DDL triggers (which can roll back operations based on the object and user).