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).

- 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>