refact: openapi splitted into separate files

api/paths/users-id.yaml

@@ -0,0 +1,26 @@
+get:
+  summary: Get user info
+  parameters:
+  - in: path
+    name: user_id
+    required: true
+    schema:
+      type: string
+  - in: query
+    name: fields
+    schema:
+      type: string
+      default: all
+  responses:
+    '200':
+      description: User info
+      content:
+        application/json:
+          schema:
+            $ref: '../schemas/User.yaml'
+    '404':
+      description: User not found
+    '400':
+      description: Request params are not correct
+    '500':
+      description: Unknown server error