feat: adaptive display of links for Quince

[DmytroAlipov]

This is a backport from the master.

Description

Do not display the 'Learn more' and 'Share feedback' links for the banner that is enabled by the context_course.discussions_settings flag if the URLs for these links are not set in the settings.

• DISCUSSIONS_INCONTEXT_LEARNMORE_URL
• DISCUSSIONS_INCONTEXT_FEEDBACK_URL

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