Changes in runtime following implementation of Session in provider

[merav-aharoni]

What is the expected feature or enhancement?
In Qiskit/qiskit-ibm-provider#675, we are supporting Session in qiskit-ibm-provider.
I am opening this issue to keep track of changes that should be done here after the above PR is complete.

• Remove utils/converters.py and import that from qiskit-ibm-provider.
• Can class Session be united between the two repos?
• Can api/rest/rutime_session.py be united between the two repos?
• Consider removing Session._circuits_map if not used
• Fix example in session.py documentation. circ is not defined.

Acceptance criteria

[jyu00]

Addition code that can probably be united:

• ibm_backend.py
• hub_group_project.py
• exception.py
• constants.py
• account management
• job
• a bunch of code in utils, like json.py, runner_result.py, etc

[merav-aharoni]

Session here cannot be united with that of qiskit-ibm-provider because here is has a QiskitRuntimeService member. However, I think we could inherit here from Session in provider. This would require changing one of the Session names. @kt474 , @jyu00 - let me know if you think this is worthwhile.

[merav-aharoni]

I am moving this list to #1028, because these duplications are not related to the implementation of Session in the provider, and uniting these files is not trivial.

[kt474]

Session here cannot be united with that of qiskit-ibm-provider because here is has a QiskitRuntimeService member. However, I think we could inherit here from Session in provider. This would require changing one of the Session names. @kt474 , @jyu00 - let me know if you think this is worthwhile.

We can focus on the other parts of this issue for now, changing one of the Session names would complicate things for users.

[kt474]

will track the remaining code duplication/consolidation in #1028