[feature] Federate pinned posts (aka featuredCollection) in and out (#1560)

* start fiddling

* the ol' fiddle + update

* start working on fetching statuses

* poopy doopy doo where r u uwu

* further adventures in featuring statuses

* finishing up

* fmt

* simply status unpin loop

* move empty featured check back to caller function

* remove unnecessary log.WithContext calls

* remove unnecessary IsIRI() checks

* add explanatory comment about status URIs

* change log level to error

* better test names

internal/api/activitypub/users/common.go

@@ -18,12 +18,14 @@
 
 package users
 
-// SwaggerCollection represents an activitypub collection.
+// SwaggerCollection represents an ActivityPub Collection.
 // swagger:model swaggerCollection
 type SwaggerCollection struct {
-	// ActivityStreams context.
+	// ActivityStreams JSON-LD context.
+	// A string or an array of strings, or more
+	// complex nested items.
 	// example: https://www.w3.org/ns/activitystreams
-	Context string `json:"@context"`
+	Context interface{} `json:"@context"`
 	// ActivityStreams ID.
 	// example: https://example.org/users/some_user/statuses/106717595988259568/replies
 	ID string `json:"id"`
@@ -55,3 +57,25 @@ type SwaggerCollectionPage struct {
 	// example: ["https://example.org/users/some_other_user/statuses/086417595981111564", "https://another.example.com/users/another_user/statuses/01FCN8XDV3YG7B4R42QA6YQZ9R"]
 	Items []string `json:"items"`
 }
+
+// SwaggerFeaturedCollection represents an ActivityPub OrderedCollection.
+// swagger:model swaggerFeaturedCollection
+type SwaggerFeaturedCollection struct {
+	// ActivityStreams JSON-LD context.
+	// A string or an array of strings, or more
+	// complex nested items.
+	// example: https://www.w3.org/ns/activitystreams
+	Context interface{} `json:"@context"`
+	// ActivityStreams ID.
+	// example: https://example.org/users/some_user/collections/featured
+	ID string `json:"id"`
+	// ActivityStreams type.
+	// example: OrderedCollection
+	Type string `json:"type"`
+	// List of status URIs.
+	// example: ['https://example.org/users/some_user/statuses/01GSZ0F7Q8SJKNRF777GJD271R', 'https://example.org/users/some_user/statuses/01GSZ0G012CBQ7TEKX689S3QRE']
+	Items []string `json:"items"`
+	// Number of items in this collection.
+	// example: 2
+	TotalItems int
+}