Uses a generic form field name for payload upload

This will facilitate a migration to a generic and API v2 compatible file
upload code in the file service.

app/api/v2/handlers/payload_api.py

@@ -67,7 +67,7 @@ async def get_payloads(self, request: web.Request):
     async def post_payloads(self, request: web.Request):
         # As aiohttp_apispec.form_schema already calls request.multipart(),
         # accessing the file using the prefilled request["form"] dictionary.
-        field_field: web.FileField = request["form"]["payload"]
+        field_field: web.FileField = request["form"]["file"]
 
         file_name, file_path = await self.__generate_file_name_and_path(field_field)
 

app/api/v2/schemas/payload_schemas.py

@@ -12,7 +12,7 @@ class PayloadSchema(schema.Schema):
 
 
 class PayloadCreateRequestSchema(schema.Schema):
-    payload = fields.Raw(type="file", required=True)
+    file = fields.Raw(type="file", required=True)
 
 
 class PayloadDeleteRequestSchema(schema.Schema):