[Task architecture] - Implement methods in `SystemContextHandle` to stop, transition and restart consensus

[ss-es]

What is this task and why do we need to work on it?

Once tasks become restartable, we should have methods in SystemContextHandle that pause a task, transition our internal state to an upgraded state and restart consensus at the new upgraded state.

What work will need to be done to complete this task?

The network tasks should be largely stateless, but some additional work may be needed to handle those too.

Are there any other details to include?

No response

What are the acceptance criteria to close this issue?

Minimally, a test should be done in e.g. the examples that consensus can be paused via the handle (though this can be a one-off, and doesn't need to be added to CI).

Branch work will be merged to (if not the default branch)

No response