`observe_value` `done_status` parameter should be removed in favour of `async with` on `Status`

[rtuck99]

Once #1012 is merged, this will implement async with on AsyncStatus which will provide a safer way of bounding the lifetime of the status-monitoring task.

Therefore done_status should be removed / deprecated in favour of async with

Acceptance Criteria

• done_status is removed as a parameter from observe_value()