Alignment option when embedding media from URL is not honoured

[robbieaverill]

Version: SS 4.3.0-rc1 (in CWP 2.2.0-rc1 context)

• Edit a page
• Click "insert media from URL"
• Enter a YouTube video URL
• Choose centre alignment
• Save the page dialog, and save the page
• Visit the page on the frontend

Expected: the video should be centre aligned

Actual: It's left aligned

Could be related to https://github.com/silverstripe/silverstripe-cms/issues/2202