get_store should have an optional store_id parameter

In the current implementation, get_store return the OpenFGA store specified in the client_api configuration.
Except by listing all the stores with list_stores, I don't see any other way to get a specific store different of the one defined in the configuration.
A way to arrange that would be to add an optional store_id parameter to get_store.

Part of https://github.com/openfga/sdk-generator/issues/118

We should do something similar to what @jimmyjames mentions here:
https://github.com/openfga/java-sdk/issues/150#issuecomment-2666996341

• for requests that use the storeId in the path, update the request options object to include a storeId
• In OpenFgaClient, if the options are not null and storeId is non-null and non-empty, use that to build the path. Otherwise, use the storeId configured on the client
• Update the tests to verify that the storeId can be overridden per request, and that the value on the client is used if not overridden.

In general, it should be pretty similar to how the authorizationModelId is allowed to be overridden per request.

Beginne mit OpenFgaClient.get_store und den von Client-Methoden verwendeten Request-Optionen. Vergleiche das bestehende Überschreibungsverhalten von authorizationModelId und prüfe anschließend die zugehörigen Tests, um zu verifizieren, dass ein storeId pro Request den konfigurierten Store überschreibt und der konfigurierte Wert als Fallback erhalten bleibt.