Instantiate a Session with an existing session id

[caleb-johnson]

What is the expected feature or enhancement?
One should be able to instantiate a Session object with an existing session id str.

Acceptance criteria
Users should have the ability to instantiate a Session object with its private _session_id attribute set.

One implementation might look like:

session_id: str = ...
session = Session.from_id(session_id)

[caleb-johnson]

One use case / need for this is: A user is submitting consecutive jobs to the backend within a session, and their local system crashes. They cannot easily instantiate a new Session object and resume their work before the timeout. They would need to use a different/more complicated interface (QiskitRuntimeService.run).

Another use case is: A user who has a Session instantiation inside a remote function. Provider is not serializable, so it is often difficult to pass Qiskit Runtime objects to cloud functions. It may require passing a QiskitRuntimeService and the Provider/Session be spun up inside the remote function.

In this scenario, a user may want to also submit a session_id to the remote function, so when they instantiate the new Session remotely, they can easily get back to the front of the queue. The service.run interface is more difficult to deal with in my experience.