refactor: deprecate socket method posts.getPidIndex

public/openapi/write/posts/pid/index.yaml

@@ -0,0 +1,28 @@
+get:
+  tags:
+    - posts
+  summary: get post index
+  description: This operation retrieves a post's index relative to its topic
+  parameters:
+    - in: path
+      name: pid
+      schema:
+        type: string
+      required: true
+      description: a valid post id
+      example: 2
+  responses:
+    '200':
+      description: Post index successfully retrieved.
+      content:
+        application/json:
+          schema:
+            type: object
+            properties:
+              status:
+                $ref: ../../../components/schemas/Status.yaml#/Status
+              response:
+                type: object
+                properties:
+                  index:
+                    type: number