[documentation] Revise the tutorials section of the docs

[laisbsc]

The tutorial section of the docs needs more love.
Opening this issue to work on:

• revise the Dask Gateway usage tutorial
• remove the double files from the docs section
• add a Pangeo tutorial (arrange with Rich Signell).

[github-actions]

This issue has been automatically marked as stale because there was no recent activity in 60 days. Remove the stale label or add a comment, otherwise, this issue will automatically be closed in 7 days if no further activity occurs.

[github-actions]

This issue was closed because it has been stalled for 7 days with no activity.