Added self link to StorageFile API representation

docs/api/apiv3/components/schemas/file_collection_model.yml

@@ -47,6 +47,9 @@ example:
         lastModifiedAt: '2021-12-20T14:00:13.987Z'
         createdByName: Luke Skywalker
         lastModifiedByName: Anakin Skywalker
+        _links:
+          self:
+            href: 'urn:openproject-org:api:v3:storages:storage_file:no_link_provided'
       - id: 1338
         location: '1338'
         name: README.md
@@ -56,3 +59,6 @@ example:
         lastModifiedAt: '2021-12-21T14:00:13.987Z'
         createdByName: Leia Organa
         lastModifiedByName: Leia Organa
+        _links:
+          self:
+            href: 'urn:openproject-org:api:v3:storages:storage_file:no_link_provided'

docs/api/apiv3/components/schemas/storage_file_location_model.yml

@@ -7,3 +7,16 @@ properties:
   location:
     type: string
     description: Location identification for file in storage
+  _links:
+    type: object
+    required:
+      - self
+    properties:
+      self:
+        allOf:
+          - "$ref": "./link.yml"
+          - description: |-
+              Not provided
+              
+              **Resource**: urn:openproject-org:api:v3:storages:storage_file:no_link_provided
+            readOnly: true

modules/storages/lib/api/v3/storage_files/storage_file_representer.rb

@@ -30,6 +30,10 @@ module API::V3::StorageFiles
   class StorageFileRepresenter < ::API::Decorators::Single
     include API::Decorators::DateProperty
 
+    link :self do
+      { href: "#{::API::V3::URN_PREFIX}storages:storage_file:no_link_provided" }
+    end
+
     property :id
     property :name
     property :size
@@ -41,7 +45,7 @@ module API::V3::StorageFiles
     property :location
 
     def _type
-      'StorageFile'
+      Storages::StorageFile.class.to_s
     end
   end
 end