Schema template --save --schema support

[simonw]

Refs:

• Template support for schemas #778

TODO:

• Consider the thing where llm -t template-with-schema hangs waiting for stdin
• Tests
• Documentation

[simonw]

OK I got this to work:

llm --schema '{                                                      
    "type": "object", 
    "properties": {
        "name": {
            "type": "string"
        },
        "bio": {
            "type": "string"
        }
    }
}' 'invent a cool dog' --save cool-dog

Then:

llm -t cool-dog