Openprompt polishing

[akvlad]

• JSON object output:

  select open_prompt('I want ice cream', json_schema := '{
     "type": "object",
     "properties": {
       "summary": { "type": "string" },
       "sentiment": { "type": "string", "enum": ["pos", "neg", "neutral"] }
     },
     "required": ["summary", "sentiment"],
     "additionalProperties": false
   }');

• custom system prompt:

  select open_prompt('I want ice cream.', system_prompt:='The respose MUST be a JSON with the following schema: {
         "type": "object",
         "properties": {
           "summary": { "type": "string" },
           "sentiment": { "type": "string", "enum": ["pos", "neg", "neutral"] }
         },
         "required": ["summary", "sentiment"],
         "additionalProperties": false
       }');