Fix Observability YouTube URL timestamp

[Jeroen-VdB]

Thank you for helping make the Dapr documentation better!

Please follow this checklist before submitting:

• Commits are signed with Developer Certificate of Origin (DCO - learn more)
• Read the contribution guide
• [ ] Commands include options for Linux, MacOS, and Windows within codetabs
• [ ] New file and folder names are globally unique
• [ ] Page references use shortcodes instead of markdown or URL links
• [ ] Images use HTML style and have alternative text
• [ ] Places where multiple code/command options are given have codetabs

In addition, please fill out the following to help reviewers understand this pull request:

Description

Updated the timestamp in the YouTube link provided on the observability page to start at the observability demo instead of the secrets management demo.

Issue reference

#4434

[marcduiker]

@holopin-bot @Jeroen-VdB Thanks Jeroen!

[holopin-bot]

Congratulations @Jeroen-VdB, the maintainer of this repository has issued you a badge! Here it is: https://holopin.io/claim/cm4873r6417160cjun1wgsmy9

This badge can only be claimed by you, so make sure that your GitHub account is linked to your Holopin account. You can manage those preferences here: https://holopin.io/account.
Or if you're new to Holopin, you can simply sign up with GitHub, which will do the trick!