Update links to the Katacoda tutorials to point to the official versions
at https://katacoda.com/tektoncd and update the dashboard scenario naming
to be consistent with other (i.e. drop the redundant `tekton-` from the
name + URL).

Update the Dashboard katacoda tutorial to use the latest releases:
- Dashboard 0.13.0
- Pipelines 0.20.0

Update screenshots to reflect the new design in recent dashboard versions.
While doing this I converted the images to JPEG for significant filesize
savings over the existing PNG images (>50% on average)

Katacoda supports linking to images in the assets folder. Update our
existing links to use this approach instead of using the GitHub 'raw'
URLs as this gives us greater portability for the tutorials and ensures
the correct version of the images is loaded even if we stop loading content
from the `master` branch in future.

- Moved over Brandow Walker's dashboard tutorial
- Created the basic pipeline tutorial
Signed-off-by: NJJ Asghar <jjasghar@gmail.com>
Co-authored-by: NBrandon Walker <bcwalker@ibm.com>