Structured Data support for the Page protocol in the Infrastructure package (#32)

This PR contains the work done to introduce a `StructuredData` type that pages use to describe themselves to search engines as schema.org JSON-LD, and wires it into the Page protocol so the payload renders automatically in the document head.

Reviewed-on: rock-n-code/loud-amsterdam#32
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>

Packages/Infrastructure/Sources/Internal/Extensions/String+Separators.swift

@@ -0,0 +1,5 @@
+extension String {
+    enum Separator {
+        static let comma = ","
+    }
+}