Bug: allow $respond to return custom Content-Type header

[dylburger]

Right now, Pipedream appends chartset=utf-8 to the Content-Type header returned with any HTTP response issued with$respond, even if I provide my own custom Content-Type header.

[jveres]

This is expected to return an image, a single red pixel.

$respond({
    status: 200,
    headers: {'Content-Type': 'image/png'}, 
    body: Buffer.from('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8DwHwAFBQIAX8jx0gAAAABJRU5ErkJggg==', 'base64').toString()
})

Not sure if charset=utf-8 is the real issue, Content-Length mismatches as well in the response: 92 instead of 70.

[casret]

The body param will now correctly handle Buffer objects (do not convert it to a string).

A pixel is too small for me too see, but:
https://pipedream.com/new?template=p_95CBwD
renders:

https://enbt2igvz16wu8n.m.pipedream.net/?pipedream_response=1