Feature request: Return raw headers from fetch response

[davidhin]

Is your feature request related to a problem? Please describe.
Currently, the response from fetch (tauri-apps/api/http) automatically parses the headers. There is a situation where the response has multiple "set-cookies" headers but fetch only returns the last one.

Describe the solution you'd like
Similar to node-fetch, allow access to the raw headers.

Describe alternatives you've considered
I've tried using other request libraries, but run into CORS issues.