Add more convenience methods

[aaronalphonso]

Description

This PR adds a number of convenience methods to the library, namely:

• CreateStore
• ListStores
• CreateAuthModel
• ListAuthModels
• GetAuthModel
• FindMatchingTuples (uses openfga.Read)
• FindUsersByRelation (uses openfga.Expand)
• FindAccessibleObjectsByRelation (uses openfga.ListObjects)
• ReadChanges

With these new convenience methods, the library covers almost all of the underlying APIs exposed by openFGA, and should allow to interact with openFGA instances for almost all desired use-cases.

Closes CSS-4329

Pending

Unit tests are pending for the all the newly added functions. I will add these in a subsequent PR.