Support importing assertions along with the store

[poovamraj]

Currently we support importing a store file using

fga import store --file=store.fga.yaml

But this doesn't import the assertions present along with the store.

Importing the assertions can be helpful to be accessed from the playground and do the checks.

[rhamzeh]

Blocked by:

• Support Contextual Tuples in Assertions API openfga#946
• Support Context in Assertions API  openfga#1353

[KamalAman]

I would also love a fga model test --upload command to upload the assertions into the playground