text: Title: [Actions][7.x] Move saved object fields to references for action_task_params
  Body: Relates to https://github.com/elastic/kibana/issues/100067
  
  To prepare for the upcoming saved object ID migration, we need to move saved object fields to use references properly so the 8.0 migration will automatically update them.
  
  We need to add a migration that will move `action_task_params.relatedSavedObjects` and `action_task_params.actionId` to saved object references. For both, there isn't exactly a 1-1 match between the data structures.
  
  For `actionId`, I'd imagine the reference object to look like: `{ id: actionId, type: 'action', name: 'action' }`
  
  For `relatedSavedObjects`, it's a little more complicated. The `id` and `type` are straight-forward, but the saved object reference requires a `name` which might map to `relatedSavedObject.typeId` or something similar. The other piece of noteworthy data is `relatedSavedObject.namespace` which I think can safely be dropped, as the `action_task_params` saved object will always exist in the same space as the action that created it.
  
  In addition to the migration, we need to change the code that [writes](https://github.com/elastic/kibana/blob/master/x-pack/plugins/actions/server/create_execute_function.ts#L64) and [reads](https://github.com/elastic/kibana/blob/master/x-pack/plugins/actions/server/lib/task_runner_factory.ts#L181).
  
  See [the PoC PR](https://github.com/elastic/kibana/pull/107611) for more insight into how this might work.