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/Tests/Utils/Pages/StubPage.swift

@@ -19,6 +19,9 @@ struct StubPage: Page {
     /// The card rendered as link-preview tags in the document head, or `nil` to omit them.
     let socialCard: SocialCard?
 
+    /// The structured data rendered as a JSON-LD script in the document head, or `nil` to omit it.
+    let structuredData: StructuredData?
+
     /// The summary rendered in the document head, or `nil` to omit it.
     let summary: String?
 
@@ -33,6 +36,8 @@ struct StubPage: Page {
     ///     to omit it.
     ///   - socialCard: the card rendered as link-preview tags in the document head, or `nil`
     ///     (the default) to omit them.
+    ///   - structuredData: the structured data rendered as a JSON-LD script in the document
+    ///     head, or `nil` (the default) to omit it.
     ///   - summary: the summary rendered in the document head, or `nil` (the default)
     ///     to omit it.
     init(
@@ -40,12 +45,14 @@ struct StubPage: Page {
         assetVersion: String? = nil,
         canonicalURL: String? = nil,
         socialCard: SocialCard? = nil,
+        structuredData: StructuredData? = nil,
         summary: String? = nil
     ) {
         self.assetVersion = assetVersion
         self.canonicalURL = canonicalURL
         self.locale = locale
         self.socialCard = socialCard
+        self.structuredData = structuredData
         self.summary = summary
     }