Use new lab endpoint to check connection liveness

[lukashornych]

In the evitaDB's lab api, there will be new endpoint /lab/liveness which will return 200 or otherwise to signalize if the new connection in evitaLab is valid. We will use this instead of fetching server status from gRPC API. The new endpoint will also internally probe the gRPC API because it is mandatory to be enabled and alive for evitaLab to function.

This will allow us to:

• verify that the user is using proxied lab URL and not gRPC API URL directly without complex verification
• check that gRPC is enabled

We will not probe other enabled APIs as errors thrown during accessing other APIs should be shown when actually accessing these APIs through UI.

[lukashornych]

Related evitaDB issue FgForrest/evitaDB#711