fix: :url property values with macros

Macros in :url are useful for having urls with a common hostname that
can be configured once. Without this fix, docs graph is invalid

deps/graph-parser/test/resources/exporter-test-graph/pages/url.md

@@ -1,4 +1,5 @@
 type:: [[Property]]
-url:: https://schema.org/url
+url:: {{docs-base-url url}}
+sameAs:: https://schema.org/url
 rangeIncludes:: [[Uri]]
 unique:: true