ADX-1087 Add Zanzibar (autonomous island in Tanzania) as location opt…

[tomeksabala]

Description

Add Zanzibar (autonomous island in Tanzania) as location option for datasets metadata. This required a custom handling of this "dummy" country in the SVG map location blueprint for the map on the ADR homepage.

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• The Jira ticket for this issue has been updated to "Ready to Review" or equivalent.
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