Link to video library in onboarding docs needs updates

[AAkindele]

The link to the video library is out of date on the onboarding documentation.

This link, https://aka.ms/k8s-videos, is the old one.

The new links can be found here. #545

• k8s upskilling Videos - https://aka.ms/rdc-k8s
• demos - https://aka.ms/rdc-demos
• archive - https://aka.ms/rdc-archive