Updated the prompt properties for Tanuki Bot

What does this MR do and why?

Updated the prompt properties for Tanuki Bot

This is to have the unified set of parameters when working with both - the documentation chat (Tanuki bot) and the Continuous chat (preserving the context)

Screenshots or screen recordings

No visual changes:

How to set up and validate locally

You will need to setup the embedding database on your GDK if you haven't already.

1. Ensure GDK has Ultimate License. Then in your terminal run

> gdk update &&. gdk config set gitlab.rails.databases.embedding.enabled true && gdk config set pgvector.enabled true && gdk reconfigure && cd gitlab && bin/rails db:migrate && rails c

2. Now, that you're in the Rails console, do:

Gitlab::CurrentSettings.update(openai_api_key: "${KEY}")
Feature.enable(:super_sidebar_nav)
Feature.enable(:openai_experimentation)
Feature.enable(:tanuki_bot)

3. Run script

Then to test (be sure to enable all the Feature Flags in the above setup to see the UI elements)

1. Ensure the New navigation is enabled. You can enable it by clicking your User profile photo in the top right and toggle the switch
2. Click the help link in the bottom left of the new Sidebar navigation
3. Click Ask GitLab Chat link
4. Ask a question
5. Ensure it works as intended (load times may be a bit long for the response)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/410557