Delete duplicated extension kinds article and add redirect to updated article

Author: bszyman

16/umbraco-cms/.gitbook.yaml

@@ -147,3 +147,4 @@ redirects:
     customizing/extending-overview/extension-registry/extension-registry: customizing/extending-overview/extension-registry/register-extensions.md
     customizing/extending-overview/extension-types/workspaces/workspace-action-menu-item: customizing/extending-overview/extension-types/workspaces/workspace-action-menu-items.md
     customizing/extending-overview/extension-types/workspaces/workspace-footer-app: customizing/extending-overview/extension-types/workspaces/workspace-footer-apps.md
+    customizing/extending-overview/extension-kind: customizing/extending-overview/extension-types/kind.md