Fix: Make swagger doc compliant to OpenAPI (#3394)

This fixes issues in the swagger.json file. The motivation to do so is to be able to generate API clients using https://openapi-generator.tech Doing so will require further changes to the api spec, but this seems like a good first step since it is now "valid" according to editor.swagger.io and openapi-generator validate.

Fixes #2806

swagger/parameters/contact_sort.yml

@@ -1,15 +1,14 @@
 in: query
 name: sort
-schema:
-  type: string
-  enum:
-    - name
-    - email
-    - phone_number
-    - last_activity_at
-    - -name
-    - -email
-    - -phone_number
-    - -last_activity_at
+type: string
+enum:
+  - name
+  - email
+  - phone_number
+  - last_activity_at
+  - -name
+  - -email
+  - -phone_number
+  - -last_activity_at
 required: false
 description: The attribute by which list should be sorted