[Feature Request] Allow the ability of sending the headers from the same route

[sansyrox]

Current Behavior

Currently, you cannot send the custom headers in the response from you route. Add the ability to do that.

Desired Behavior

Something along these lines, from our discussion on discord with @cirospaciari

@app.get('/plaintext')
def plaintext() -> str:
    return { "body": "Hello, world!", "headers": { "Content-Type": "plain/text", "Custom": "My Custom Value" }}  

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Screenshots / Mockups

Alternatives

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