Provide a config form for brand voice override

Problem/Motivation

Currently brand voice guidelines has to be set through code using the hook hook_ai_brand_voice_alter.
It would probably be easier if there was a config form for the same.
That would be beneficial to Drupal CMS users, where we are expecting the environment to be low-code.

Steps to reproduce

NA

Proposed resolution

Provide a config form for providing the brand voice guidelines.

Remaining tasks

NA

User interface changes

NA

API changes

NA

Data model changes

NA