Add generic type for the send method

[joetannenbaum]

This PR adds a generic type to the stream hooks that allows the user to specify the shape of the send method:

const { send } = useStream<{ messages: string[]}>();

send({
    messages: ['first', 'second', 'third']
})

It includes one small breaking change: Previously, the first generic type passed into useStream was to specify the JSON shape if using the json option, now the send payload is the first generic and the JSON shape is the second.

For useJsonStream the JSON payload remains the first generic, the send payload is the now the second.