Review how execution events are fetched

For now, the fetching of execution events is done as so:

• When mounting WorkflowList, all execution events are fetched and cached with rest-hooks.
• When receiving a new execution event though the socket, this cache is invalidated meaning that all executions events are refetched.

While this worked for a prototype version, this is far from being optimized. For this, it is important to note that events are fetched as an array of lists, each list being associated to a single job:

[
  [{job_id: 1, type: start}, ..., {job_id: 1, type: end}],
  [{job_id: 2, type: start}, ..., {job_id: 2, type: end}],
  ...
  [{job_id: N, type: start}, ..., {job_id: N, type: end}],
]

WorkflowList renders a WorkflowItem per job_id. WorkflowItem takes care of parsing the list of job events to display the appropriate info.

Ideally I would like to:

• Fetch all execution events when mounting WorkflowList and cache them.
• Rerender WorkflowList when receiving a new execution event though the socket that has a new job_id. This is to create the new WorkflowItem component associated to the new job_id
• Rerender only the associated WorkflowItem when receiving a new execution event though the socket with an exisiting job_id.