update schema for job args s.t. types can be strings and scalars

Right now, job args are being serialized as strings. For proper deserialization, args should be serialized as scalars or strings. https://docs.google.com/document/d/1URPG6SLG481Y7DDAajjVtedKjS5pwIQ41UOhwSQYbhk/edit#bookmark=id.nxxgygfmgu2k