Instantiate a Session with an existing session id

**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)
```