[AI][Finetune] Finetune training and usage cost if any

[yellow1912]

Proposed changes

• https://developers.cloudflare.com/workers-ai/fine-tunes/
  The document mentions the ability to fine-tune with our custom data, but it's unclear about the cost of training and using the adapters if any

Subject Matter

Finetune training and usage cost

Content Location

I expect it to be a separated section on this page:

https://developers.cloudflare.com/workers-ai/fine-tunes/

It should also be mentioned here on this page:

https://developers.cloudflare.com/workers-ai/platform/pricing/

Additional information

No response