Add missing instances schemas

Add the missing OpenAPI instances schemas

Author: m-burgoyne

core/standard/openapi/schemas/collections/collection.yaml

@@ -106,6 +106,11 @@ properties:
         properties:
           link:
             $ref: itemsLink.yaml
+      instances:
+        type: object
+        properties:
+          link:
+            $ref: instancesLink.yaml          
   crs:
     description: list of the coordinate reference systems the collection results can support
     type: array

core/standard/openapi/schemas/collections/instancesDataQuery.yaml

@@ -0,0 +1,18 @@
+description: Property to contain any extra metadata information that is specific
+  to an individual data queries
+type: object
+properties:
+  title:
+    description: title of the query
+    type: string
+    example: Instances query
+  description:
+    description: description of the query
+    type: string
+    example: Instances of collection each representing different versions
+  query_type:
+    description: Instances of collection
+    type: string
+    enum: 
+      - instances
+    example: instances

core/standard/openapi/schemas/collections/instancesLink.yaml

@@ -0,0 +1,8 @@
+allOf:
+  - $ref: ../core/link.yaml
+properties:
+  href:
+    type: string
+    example: https://example.com/collections/monitoringsites/instances
+  variables:
+    $ref: instancesDataQuery.yaml