[DEV DOCS] Journey of a task - HLG edition

The distributed documentation offers a [Journey of a Task](https://distributed.dask.org/en/stable/journey.html) entry outlining how a `client.submit` is serialized, submitted to the scheduler, handled, computed, etc. up until the task is forgotten.

When using dask collections we are typically not directly using `client.submit` and this journey might look drastically different, especially when using High Level Graphs.

https://github.com/dask/community/issues/190#issuecomment-941235626

see also https://github.com/dask/dask/issues/7709