feat: Support MultipartRequest in functions invoke

[Vinzent03]

What kind of change does this PR introduce?

feature

What is the current behavior?

The body can only be of type Map<String,dynamic> and no files can be uploaded.

What is the new behavior?

The body can be any Object, which is encodable to String. There's now a files parameter to send files with a MultipartRequest.

Additional context

At the moment everything is bundled in one method like in functions-js. One could argue to create an extra method to be more type safe with body being Map<String,String>.

close #933

[dshukertjr]

This is great! We probably need to export MultipartFile so that it's available to the users, right?

[Vinzent03]

It's from the http package, which I guess most people have already installed and can import themself. But exporting just that class won't hurt, so I will add that tomorrow.

[dshukertjr]

It's from the http package, which I guess most people have already installed and can import themself. But exporting just that class won't hurt, so I will add that tomorrow.

Awesome 👍 Just sharing my two cents, but I think it's common for people to not have the HTTP package installed if they are using Supabase.

[Vinzent03]

Since more types for the body are allowed now, I've added a basic content header detection. For string inputs, it sets the header to text/plain and for Uint8List as an example for binary data to octet stream.

[dshukertjr]

Love the automatic content type detection!