Print the instance used to connect or run on the service

[francabrera]

What is the expected feature or enhancement?

When connecting to the quantum channel, when the user doesn't specifying an instance or they have setup the environment variable QISKIT_IBM_INSTANCE, it's hard to tell which instance the provider chose so I have no clue which instance I'm using.

Acceptance criteria

When connecting to the service, if one instance is selected (including by the env variable or when the user specifies one programatically), print it. When running a job print which instance it's using.

[jyu00]

When running a job print which instance it's using.

I don't think we need this at every job run, since that can get annoying quickly. Probably just once at service initialization (if instance is not explicitly specified), and at job run if the instance used is different (e.g. we need to switch to a different one to access the backend selected).