Multiple "set-cookie" header are overwritten by the "supervisord"

[Alie.E]

Several "set-cookie" headers are allowed by RFC6265:
https://datatracker.ietf.org/doc/html/rfc6265#section-3

vm_supervisord should correctly handle "set-cookie" headers:

aleph-vm/vm_supervisor/run.py

Line 137 in 40c5c5b

 key.decode(): value.decode() for key, value in result["headers"]["headers"] 

[Hugo Herter]

This should probably use a https://multidict.aio-libs.org/en/stable/multidict.html#multidict.CIMultiDictProxy

[Alie.E]

merged: #327