add option to retrieve stored ibm credentials

[richrines1]

What is happening?

i can instantiate a QiskitRuntimeService() / IBMProvider() without any arguments because my credentials are already saved in a dot file. it would be nice if i could automatically use the same credentials when i instantiate a qss.SuperstaqProvider or css.Service(), instead of having to pass everything in manually

imo this shouldn't happen by default though - maybe we could either (1) allow the user to pass in a provider object/runtime service instead of individual credentials, (2) add an argument like use_stored_ibmq_credentials=False, or (3) some combination of these and a flag allowing the automatic reading of ibm configs that we put in our own config file?

What are the current alternatives?

No response

Any additional context?

No response