UX for video embed links

Rewriting this issue. After some digging, @briaguya found that he was able to troubleshoot on staging with a no-code solution.

In short: the URLs you used pointed to the video at the playlist URL, and Wagtail's video embed gets confused whenever you point to any sort of playlist.

This is definitely a user experience we can/should improve for the future.

### Temporary solution
For now, always use the link from the "share" modal on YouTube

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# Background

## Describe the bug
When I look at the preview page for "Know your rights," the four different video embeds display correctly on the page editor in Joplin. On Janis, though, the only video that shows up in all four of the embeds is the first one.

This page has not yet been approved for publishing, so if we want to see whether the error also displays on a live page, let's not not do it in production.

## URL
Preview page: https://alpha.austin.gov/en/preview/information/UGFnZVJldmlzaW9uTm9kZToyMzY3
Joplin page: https://joplin.herokuapp.com/admin/pages/265/edit/#tab-content

## To Reproduce
Steps to reproduce the behavior
example:
1. Go to 'https://alpha.austin.gov/en/preview/information/UGFnZVJldmlzaW9uTm9kZToyMzY3'
2. Log into Joplin and compare with the page editor: https://joplin.herokuapp.com/admin/pages/265/edit/#tab-content
3. Check links in Joplin. 🤔

## Current behavior
See above

## Expected behavior
I expect the video embeds to look the same in Joplin as on the preview page on Janis.

## Screenshots
Joplin page editor:

Janis preview page:

## Device and browser
Firefox 70, Macbook air

## Additional context
Doesn't look good with stakeholders who review and approve the page so we can publish it.