[CORL-3207] update wording for media links configuration

[nick-funk]

What does this PR do?

Under Configure > General for embeds, change:

• "Allow commenters to add a YouTube video, X post or GIF's to the end of their comment"
  to
• "Allow commenters to add a single piece of embedded media to the end of a comment"

These changes will impact:

• commenters
• moderators
• admins
• developers

What changes to the GraphQL/Database Schema does this PR introduce?

None

Does this PR introduce any new environment variables or feature flags?

No

If any indexes were added, were they added to INDEXES.md?

N/A

How do I test this PR?

Check wording in Config > General

Were any tests migrated to React Testing Library?

No

How do we deploy this PR?

• merge into develop

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