Pricing for AI providers, features and models

[brainless]

As a user I would like to have pricing information when selecting an AI model. This will need to be stored per model and shown in the UI where I select AI model for chat.

[brainless]

This will relate to #116 so that we organise all the information in a DRY manner and features are exposed through Rust, keeping in mind that some providers or features or models may not be available depending on API keys enabled or permissions.

Some UX to consider:

• Show feature and model pricing per provider even if they are not enabled
• Show price comparisons for similar features

Some future ideas:

• Show free tiers for providers
• Show account usage
• Show account credits

[brainless]

AI Models are better codified in Rust now. We have to still add actual pricing information per model.