Custom PromptLFile type

[csansoon]

Added a custom opt-in PromptLFile type.

If a user, before rendering a prompt, adapts all of their File parameters to a PromptLFile, using the handy toPromptLFile method, PromptL will automatically insert them as content items of the message with the correct mime type and contents. There is no need for the user to specify any content tags in the prompt!

<user>
    Take a look at this pdf:
    {{ pdf }}
    What it is about?
</user>

const pdf = toPromptLFile({ file, url })
const { messages } = await render({ prompt, parameters: { pdf } })

(Pseudo-code) OUTPUT:

<message role="user">
    <content-text>
        Take a look at this pdf:
    </content-text>

    <content-file mime="application/pdf">
        https://source/file.pdf
    </content-file>

    <content-text>
        What it is about?
    </content-text>
</message>

Additionally, some attributes can be used in the prompt too:

Look at this file: {{ file }}

It should be of type {{ file.type }}, be {{ file.size }}B and hosted at {{ file.url }}

closes: latitude-dev/latitude-llm#959