[Bug]: Future migrations for attribute-references

[jsmassa]

What version of Datahike are you using?

0.4.1489

What version of Java are you using?

openjdk 11.0.13 2021-10-19

What operating system are you using?

Ubuntu

What database EDN configuration are you using?

{:attribute-refs? true}

Describe the bug

The export for reference databases doesn't export system datoms, which then cannot be read in during the import and used to set the system schema. At the moment it works as it is now, but in case the system entities change, we will run into issues.

What is the expected behaviour?

The system entities are also exported and the import of reference databases sets the system schema just as it currently sets the user schema from datoms.

How can the behaviour be reproduced?

Change the order of the system entities between export and import and see what happens.