prefer additive changes, backward compatible -> keeping structure
as it was, but with adding new fields (that can be ignored by old
mobile clients)
in case it is impossible, and we are doing backward
incompatible change: we have a collection in Firestore, called 'versioning', where store clients with allowed versions. Then mobile application on lunch fetch this version for current platform and compare version from configuration with stored in Firestore - if version is less then min allowed, force upgrade required, else if version less then current, we recommend updating the client, otherwise all is fine.