adding rank_eval indices api specs

Signed-off-by: Tokesh <[email protected]>

spec/schemas/_core.rank_eval.yaml

@@ -134,7 +134,7 @@ components:
           additionalProperties:
             type: object
             additionalProperties:
-              type: object
+              type: number
       required:
         - hits
         - metric_details

tests/default/indices/rank_eval.yaml

@@ -0,0 +1,66 @@
+$schema: ../../../json_schemas/test_story.schema.yaml
+
+description: Test rank evaluation API using both GET and POST methods.
+epilogues:
+  - path: /movies
+    method: DELETE
+    status: [200, 404]
+prologues:
+  - path: /_bulk
+    method: POST
+    parameters:
+      refresh: true
+    request:
+      content_type: application/x-ndjson
+      payload:
+        - {create: {_index: movies, _id: movie1}}
+        - {director: Quentin Tarantino, title: Pulp Fiction, year: 1994}
+        - {create: {_index: movies, _id: movie2}}
+        - {director: Christopher Nolan, title: Inception, year: 2010}
+
+chapters:
+  - synopsis: Perform rank evaluation using GET.
+    path: /{index}/_rank_eval
+    method: GET
+    parameters:
+      index: movies
+    request:
+      payload:
+        metric:
+          precision:
+            k: 10
+        requests:
+          - id: "query_1"
+            request: 
+              query: 
+                match: 
+                  title: "Pulp Fiction"
+            ratings: 
+              - _id: "movie1"
+                rating: 1
+                _index: movies
+    response:
+      status: 200
+
+  - synopsis: Perform rank evaluation using POST.
+    path: /{index}/_rank_eval
+    method: POST
+    parameters:
+      index: [movies]
+    request:
+      payload:
+        metric:
+          mean_reciprocal_rank:
+            k: 10
+        requests:
+          - id: "query_2"
+            request: 
+              query: 
+                match: 
+                  director: "Christopher Nolan"
+            ratings: 
+              - _id: "movie2"
+                _index: movies
+                rating: 1
+    response:
+      status: 200