Import assertions when importing store

[sujitha-av]

Description

When importing a store, we usually import the model and the tuples from the file. But these changes enable us to also import the assertions (only Check assertions) from the Model Tests as a part of the store import.

References

Open issue - 224

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[sujitha-av]

fixing the linting tomorrow

[sujitha-av]

need some help with this - running golangci-lint gives
cmd/store/import_test.go:7:1: File is not properly formatted (goimports)
but running goimports separately does not seem to be catching this.