FEATURE: allow personas to supply top_p and temperature params (#459)

* FEATURE: allow personas to supply top_p and temperature params

Code assistance generally are more focused at a lower temperature
This amends it so SQL Helper runs at 0.2 temperature vs the more
common default across LLMs of 1.0.

Reduced temperature leads to more focused, concise and predictable
answers for the SQL Helper

* fix tests

* This is not perfect, but far better than what we do today

Instead of fishing for

1. Draft sequence
2. Draft body

We skip (2), this means the composer "only" needs 1 http request to
open, we also want to eliminate (1) but it is a bit of a trickier
core change, may figure out how to pull it off (defer it to first draft save)

Value of bot drafts < value of opening bot conversations really fast

test/javascripts/unit/models/ai-persona-test.js

@@ -39,6 +39,8 @@ module("Discourse AI | Unit | Model | ai-persona", function () {
       system_prompt: "System Prompt",
       priority: false,
       description: "Description",
+      top_p: 0.8,
+      temperature: 0.7,
     };
 
     const aiPersona = AiPersona.create({ ...properties });
@@ -63,6 +65,8 @@ module("Discourse AI | Unit | Model | ai-persona", function () {
       system_prompt: "System Prompt",
       priority: false,
       description: "Description",
+      top_p: 0.8,
+      temperature: 0.7,
     };
 
     const aiPersona = AiPersona.create({ ...properties });