chore: update tutorial card thumbnail & video links

[tianrunhe]

Description

Request from here

• Change sprint poker tutorial video URL
• Update thumbnails

Demo

Testing scenarios

• New user sign up
  • Sign up as a new user
  • See the meeting dashboard's new tutorial cards
  • Verify the YouTube link point to the right video

Final checklist

• I checked the code review guidelines
• I have added Metrics Representative as reviewer(s) if my PR invovles metrics/data/analytics related changes
• I have performed a self-review of my code, the same way I'd do it for any other team member
• I have tested all cases I listed in the testing scenarios and I haven't found any issues or regressions
• Whenever I took a non-obvious choice I added a comment explaining why I did it this way
• I added the label Skip Maintainer Review Indicating the PR only requires reviewer review and can be merged right after it's approved if the PR introduces only minor changes, does not contain any architectural changes or does not introduce any new patterns and I think one review is sufficient'
• PR title is human readable and could be used in changelog

[nickoferrall]

IT looks good and the video links work for me, but I think we should add a video tutorial of a retro meeting too with this video that Emily created: https://www.youtube.com/watch?v=C96fNtypaww