2.1.3: Update Compact YouTube link, add Cloud Run container caching note

Version: 2.1.3

Notable Changes:

• Added a note about Cloud Run's container caching and its effects
• Adjusted Compact YouTube link

Explanations of Changes (if Needed):

I have changed Compact YouTube to use a custom domain and updated the link to point to the new domain.

I also encountered an error while deploying 2.1.2 - Cloud Run had 2.1.0's container cached, so I had to manually redeploy it to get it to update. I added a note about this corner case (it makes me wonder if this could be exploited for free container storage...).

Merge Checklist:

• Changelog entry
• Changes tested (if needed)
• Documentation updated (if needed)
• Readme updated (if needed)
• Translations file header has version bumped
• Translations file application footer has version bumped
• Translations have been recompiled
• Unnecessary git tags for previous commits in this MR removed (git tag -d vX.Y.Z, git push --delete origin vX.Y.Z)
• Git tag created for final commit prior to merge (git tag vX.Y.Z)
• Git tag pushed (git push origin vX.Y.Z)
• CI pipeline passed on final commit prior to merge