feat(grammar): support models with specific construct (#2291)

When enabling grammar with functions, it might be useful to
allow more flexibility to support models that are fine-tuned against returning
function calls of the form of { "name": "function_name", "arguments" {...} }
rather then { "function": "function_name", "arguments": {..} }.

This might call out to a more generic approach later on, but for the moment being we can easily support both
as we have just to specific different types.

If needed we can expand on this later on

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