feat(api): support 'reasoning' api field (#7959)

This PR adds support to support the 'reasoning' API field of the OpenAI
spec.

LocalAI now will extract automatically thinking tags in both SSE and
non-SSE mode. The changes are adapted as well to the Chat UI now that
will use the reasoning field to extract the thinking process and display
it in the chat.

This fixes https://github.com/mudler/LocalAI/issues/7944

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>