fix: share certificate in FB

[DmytroAlipov]

This is a Backport from the master branch.

Fixed an issue where the Course Card Image was missing in an FB post after a user shared it.

Description

In order to share the certificate on your Facebook page, the code was used
FaceBook.share({share_text: '${facebook_share_text | n, js_escaped_string}', share_link: '${share_url | n, js_escaped_string}', picture_link: '${full_course_image_url | n, js_escaped_string}', description: '${_('Click the link to see my certificate.') | n, js_escaped_string}'});
In this case, the picture that was transmit in the picture_link parameter was ignored.

During the investigation, it was revealed that Facebook changed the rules for sharing. Meta tags must be used (follow FB rules).
After making changes to the code, the Course Card Image is displayed when you share the certificate.
In Studio:

In FB:

Sharing Debugger was used for debugging.
The default image is /static/studio/images/pencils.jpg if the course image is not loaded. Displayed as:

NOTE: og:url and share_link are the same. The "share to FB" button will not work without share_link: '${share_url | n, js_escaped_string}'. But if you do not specify og:url, the FB debugger asks you to specify the entire set of meta tags. If you do not pass og:url there will be no errors, but I decided to do as FB recommends.

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[e0d]

Will merge after this lands on master.

[DmytroAlipov]

in the master was merged

[mphilbrick211]

@e0d - is this something you can merge for us now that the master has been merged?

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