discourse / discourse

#11253)

* FEATURE: display error if Oneboxing fails due to HTTP error

- display warning if onebox URL is unresolvable
- display warning if attributes are missing

* FEATURE: Use new Instagram oEmbed endpoint if access token is configured

Instagram requires an Access Token to access their oEmbed endpoint. The requirements (from https://developers.facebook.com/docs/instagram/oembed/) are as follows:

- a Facebook Developer account, which you can create at developers.facebook.com
- a registered Facebook app
- the oEmbed Product added to the app
- an Access Token
- The Facebook app must be in Live Mode

The generated Access Token, once added to SiteSetting.facebook_app_access_token, will be passed to onebox. Onebox can then use this token to access the oEmbed endpoint to generate a onebox for Instagram.

* DEV: update user agent string

* DEV: don’t do HEAD requests against news.yahoo.com

* DEV: Bump onebox version from 2.1.5 to 2.1.6

* DEV: Avoid re-reading templates

* DEV: Tweaks to onebox mustache templates

* DEV: simplified error message for missing onebox data

* Apply suggestions from code review
Co-authored-by: Gerhard Schlager <mail@gerhard-schlager.at>