* Rename OpenAIProcessorConversationConfig to more apt AiModelAPI
The DB model name had drifted from what it is being used for,
a general chat api provider that supports other chat api providers like
anthropic and google chat models apart from openai based chat models.
This change renames the DB model and updates the docs to remove this
confusion.
Using Ai Model Api we catch most use-cases including chat, stt, image generation etc.
This is an initial pass to add documentation for all the knobs
available on the Khoj Admin panel.
It should shed some light onto what each admin setting is for and how
they can be customized when self hosting.
Resolves#831