[Feat] index.rst: Embed YT video: OpenCV Weekly Webinar Ep.49

[gmacario]

Closes #

📑 Description

Now that the recording of OpenCV Weekly Episode 49 is on YouTube, let's feature it on the ARNEIS.RTD homepage.

✅ Checks

• [x] My pull request adheres to the code style of this project
• [ ] My code requires changes to the documentation
• [x] I have updated the documentation as required
• [x] All the tests have passed

ℹ Additional Information