This PR introduces a new Recoil state to store the flow.
A few parts of the application need to know the definition of the
current flow. Previously, we stored the workflow version's ID and
fetched its definition with the `useWorkflowVersion` hook. However, we
must use another strategy to visualize workflow runs. Indeed, we now
store the definition of the workflow in the workflow run output when it
is executed. This is useful for draft versions, which can change between
the moment they were executed and the moment they are visualized.
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